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[PATCH] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()

Yu Kuai posted 1 patch 11 months, 2 weeks ago 
block/bfq-iosched.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
[PATCH] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()
Posted by Yu Kuai 11 months, 2 weeks ago 
From: Yu Kuai <yukuai3@huawei.com>

Our syzkaller report a following UAF for v6.6:

BUG: KASAN: slab-use-after-free in bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958
Read of size 8 at addr ffff8881b57147d8 by task fsstress/232726

CPU: 2 PID: 232726 Comm: fsstress Not tainted 6.6.0-g3629d1885222 #39
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x91/0xf0 lib/dump_stack.c:106
 print_address_description.constprop.0+0x66/0x300 mm/kasan/report.c:364
 print_report+0x3e/0x70 mm/kasan/report.c:475
 kasan_report+0xb8/0xf0 mm/kasan/report.c:588
 hlist_add_head include/linux/list.h:1023 [inline]
 bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958
 bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
 bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
 blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
 blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
 __submit_bio+0xa0/0x6b0 block/blk-core.c:639
 __submit_bio_noacct_mq block/blk-core.c:718 [inline]
 submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
 submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
 __ext4_read_bh fs/ext4/super.c:205 [inline]
 ext4_read_bh+0x15e/0x2e0 fs/ext4/super.c:230
 __read_extent_tree_block+0x304/0x6f0 fs/ext4/extents.c:567
 ext4_find_extent+0x479/0xd20 fs/ext4/extents.c:947
 ext4_ext_map_blocks+0x1a3/0x2680 fs/ext4/extents.c:4182
 ext4_map_blocks+0x929/0x15a0 fs/ext4/inode.c:660
 ext4_iomap_begin_report+0x298/0x480 fs/ext4/inode.c:3569
 iomap_iter+0x3dd/0x1010 fs/iomap/iter.c:91
 iomap_fiemap+0x1f4/0x360 fs/iomap/fiemap.c:80
 ext4_fiemap+0x181/0x210 fs/ext4/extents.c:5051
 ioctl_fiemap.isra.0+0x1b4/0x290 fs/ioctl.c:220
 do_vfs_ioctl+0x31c/0x11a0 fs/ioctl.c:811
 __do_sys_ioctl fs/ioctl.c:869 [inline]
 __se_sys_ioctl+0xae/0x190 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x78/0xe2

Allocated by task 232719:
 kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 __kasan_slab_alloc+0x87/0x90 mm/kasan/common.c:328
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook mm/slab.h:768 [inline]
 slab_alloc_node mm/slub.c:3492 [inline]
 kmem_cache_alloc_node+0x1b8/0x6f0 mm/slub.c:3537
 bfq_get_queue+0x215/0x1f00 block/bfq-iosched.c:5869
 bfq_get_bfqq_handle_split+0x167/0x5f0 block/bfq-iosched.c:6776
 bfq_init_rq+0x13a4/0x17a0 block/bfq-iosched.c:6938
 bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
 bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
 blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
 blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
 __submit_bio+0xa0/0x6b0 block/blk-core.c:639
 __submit_bio_noacct_mq block/blk-core.c:718 [inline]
 submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
 submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
 __ext4_read_bh fs/ext4/super.c:205 [inline]
 ext4_read_bh_nowait+0x15a/0x240 fs/ext4/super.c:217
 ext4_read_bh_lock+0xac/0xd0 fs/ext4/super.c:242
 ext4_bread_batch+0x268/0x500 fs/ext4/inode.c:958
 __ext4_find_entry+0x448/0x10f0 fs/ext4/namei.c:1671
 ext4_lookup_entry fs/ext4/namei.c:1774 [inline]
 ext4_lookup.part.0+0x359/0x6f0 fs/ext4/namei.c:1842
 ext4_lookup+0x72/0x90 fs/ext4/namei.c:1839
 __lookup_slow+0x257/0x480 fs/namei.c:1696
 lookup_slow fs/namei.c:1713 [inline]
 walk_component+0x454/0x5c0 fs/namei.c:2004
 link_path_walk.part.0+0x773/0xda0 fs/namei.c:2331
 link_path_walk fs/namei.c:3826 [inline]
 path_openat+0x1b9/0x520 fs/namei.c:3826
 do_filp_open+0x1b7/0x400 fs/namei.c:3857
 do_sys_openat2+0x5dc/0x6e0 fs/open.c:1428
 do_sys_open fs/open.c:1443 [inline]
 __do_sys_openat fs/open.c:1459 [inline]
 __se_sys_openat fs/open.c:1454 [inline]
 __x64_sys_openat+0x148/0x200 fs/open.c:1454
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x78/0xe2

Freed by task 232726:
 kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x50 mm/kasan/generic.c:522
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 __kasan_slab_free+0x12a/0x1b0 mm/kasan/common.c:244
 kasan_slab_free include/linux/kasan.h:164 [inline]
 slab_free_hook mm/slub.c:1827 [inline]
 slab_free_freelist_hook mm/slub.c:1853 [inline]
 slab_free mm/slub.c:3820 [inline]
 kmem_cache_free+0x110/0x760 mm/slub.c:3842
 bfq_put_queue+0x6a7/0xfb0 block/bfq-iosched.c:5428
 bfq_forget_entity block/bfq-wf2q.c:634 [inline]
 bfq_put_idle_entity+0x142/0x240 block/bfq-wf2q.c:645
 bfq_forget_idle+0x189/0x1e0 block/bfq-wf2q.c:671
 bfq_update_vtime block/bfq-wf2q.c:1280 [inline]
 __bfq_lookup_next_entity block/bfq-wf2q.c:1374 [inline]
 bfq_lookup_next_entity+0x350/0x480 block/bfq-wf2q.c:1433
 bfq_update_next_in_service+0x1c0/0x4f0 block/bfq-wf2q.c:128
 bfq_deactivate_entity+0x10a/0x240 block/bfq-wf2q.c:1188
 bfq_deactivate_bfqq block/bfq-wf2q.c:1592 [inline]
 bfq_del_bfqq_busy+0x2e8/0xad0 block/bfq-wf2q.c:1659
 bfq_release_process_ref+0x1cc/0x220 block/bfq-iosched.c:3139
 bfq_split_bfqq+0x481/0xdf0 block/bfq-iosched.c:6754
 bfq_init_rq+0xf29/0x17a0 block/bfq-iosched.c:6934
 bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
 bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
 blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
 blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
 __submit_bio+0xa0/0x6b0 block/blk-core.c:639
 __submit_bio_noacct_mq block/blk-core.c:718 [inline]
 submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
 submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
 __ext4_read_bh fs/ext4/super.c:205 [inline]
 ext4_read_bh+0x15e/0x2e0 fs/ext4/super.c:230
 __read_extent_tree_block+0x304/0x6f0 fs/ext4/extents.c:567
 ext4_find_extent+0x479/0xd20 fs/ext4/extents.c:947
 ext4_ext_map_blocks+0x1a3/0x2680 fs/ext4/extents.c:4182
 ext4_map_blocks+0x929/0x15a0 fs/ext4/inode.c:660
 ext4_iomap_begin_report+0x298/0x480 fs/ext4/inode.c:3569
 iomap_iter+0x3dd/0x1010 fs/iomap/iter.c:91
 iomap_fiemap+0x1f4/0x360 fs/iomap/fiemap.c:80
 ext4_fiemap+0x181/0x210 fs/ext4/extents.c:5051
 ioctl_fiemap.isra.0+0x1b4/0x290 fs/ioctl.c:220
 do_vfs_ioctl+0x31c/0x11a0 fs/ioctl.c:811
 __do_sys_ioctl fs/ioctl.c:869 [inline]
 __se_sys_ioctl+0xae/0x190 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x78/0xe2

commit 1ba0403ac644 ("block, bfq: fix uaf for accessing waker_bfqq after
splitting") fix the problem that if waker_bfqq is in the merge chain,
and current is the only procress, waker_bfqq can be freed from
bfq_split_bfqq(). However, the case that waker_bfqq is not in the merge
chain is missed, and if the procress reference of waker_bfqq is 0,
waker_bfqq can be freed as well.

Fix the problem by checking procress reference if waker_bfqq is not in
the merge_chain.

Fixes: 1ba0403ac644 ("block, bfq: fix uaf for accessing waker_bfqq after splitting")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/bfq-iosched.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 068c63e95738..c69e9faad15a 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -6844,16 +6844,24 @@ static struct bfq_queue *bfq_waker_bfqq(struct bfq_queue *bfqq)
 		if (new_bfqq == waker_bfqq) {
 			/*
 			 * If waker_bfqq is in the merge chain, and current
-			 * is the only procress.
+			 * is the only procress, waker_bfqq can be freed.
 			 */
 			if (bfqq_process_refs(waker_bfqq) == 1)
 				return NULL;
-			break;
+
+			return waker_bfqq;
 		}
 
 		new_bfqq = new_bfqq->new_bfqq;
 	}
 
+	/*
+	 * If waker_bfqq is not in the merge chain, and it's procress reference
+	 * is 0, waker_bfqq can be freed.
+	 */
+	if (bfqq_process_refs(waker_bfqq) == 0)
+		return NULL;
+
 	return waker_bfqq;
 }
 
-- 
2.39.2
Re: [PATCH] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()
Posted by Jan Kara 11 months, 2 weeks ago 
On Wed 08-01-25 16:41:48, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> Our syzkaller report a following UAF for v6.6:
> 
> BUG: KASAN: slab-use-after-free in bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958
> Read of size 8 at addr ffff8881b57147d8 by task fsstress/232726
> 
> CPU: 2 PID: 232726 Comm: fsstress Not tainted 6.6.0-g3629d1885222 #39
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x91/0xf0 lib/dump_stack.c:106
>  print_address_description.constprop.0+0x66/0x300 mm/kasan/report.c:364
>  print_report+0x3e/0x70 mm/kasan/report.c:475
>  kasan_report+0xb8/0xf0 mm/kasan/report.c:588
>  hlist_add_head include/linux/list.h:1023 [inline]
>  bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958
>  bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
>  bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
>  blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
>  blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
>  __submit_bio+0xa0/0x6b0 block/blk-core.c:639
>  __submit_bio_noacct_mq block/blk-core.c:718 [inline]
>  submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
>  submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
>  __ext4_read_bh fs/ext4/super.c:205 [inline]
>  ext4_read_bh+0x15e/0x2e0 fs/ext4/super.c:230
>  __read_extent_tree_block+0x304/0x6f0 fs/ext4/extents.c:567
>  ext4_find_extent+0x479/0xd20 fs/ext4/extents.c:947
>  ext4_ext_map_blocks+0x1a3/0x2680 fs/ext4/extents.c:4182
>  ext4_map_blocks+0x929/0x15a0 fs/ext4/inode.c:660
>  ext4_iomap_begin_report+0x298/0x480 fs/ext4/inode.c:3569
>  iomap_iter+0x3dd/0x1010 fs/iomap/iter.c:91
>  iomap_fiemap+0x1f4/0x360 fs/iomap/fiemap.c:80
>  ext4_fiemap+0x181/0x210 fs/ext4/extents.c:5051
>  ioctl_fiemap.isra.0+0x1b4/0x290 fs/ioctl.c:220
>  do_vfs_ioctl+0x31c/0x11a0 fs/ioctl.c:811
>  __do_sys_ioctl fs/ioctl.c:869 [inline]
>  __se_sys_ioctl+0xae/0x190 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
>  entry_SYSCALL_64_after_hwframe+0x78/0xe2
> 
> Allocated by task 232719:
>  kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
>  kasan_set_track+0x25/0x30 mm/kasan/common.c:52
>  __kasan_slab_alloc+0x87/0x90 mm/kasan/common.c:328
>  kasan_slab_alloc include/linux/kasan.h:188 [inline]
>  slab_post_alloc_hook mm/slab.h:768 [inline]
>  slab_alloc_node mm/slub.c:3492 [inline]
>  kmem_cache_alloc_node+0x1b8/0x6f0 mm/slub.c:3537
>  bfq_get_queue+0x215/0x1f00 block/bfq-iosched.c:5869
>  bfq_get_bfqq_handle_split+0x167/0x5f0 block/bfq-iosched.c:6776
>  bfq_init_rq+0x13a4/0x17a0 block/bfq-iosched.c:6938
>  bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
>  bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
>  blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
>  blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
>  __submit_bio+0xa0/0x6b0 block/blk-core.c:639
>  __submit_bio_noacct_mq block/blk-core.c:718 [inline]
>  submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
>  submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
>  __ext4_read_bh fs/ext4/super.c:205 [inline]
>  ext4_read_bh_nowait+0x15a/0x240 fs/ext4/super.c:217
>  ext4_read_bh_lock+0xac/0xd0 fs/ext4/super.c:242
>  ext4_bread_batch+0x268/0x500 fs/ext4/inode.c:958
>  __ext4_find_entry+0x448/0x10f0 fs/ext4/namei.c:1671
>  ext4_lookup_entry fs/ext4/namei.c:1774 [inline]
>  ext4_lookup.part.0+0x359/0x6f0 fs/ext4/namei.c:1842
>  ext4_lookup+0x72/0x90 fs/ext4/namei.c:1839
>  __lookup_slow+0x257/0x480 fs/namei.c:1696
>  lookup_slow fs/namei.c:1713 [inline]
>  walk_component+0x454/0x5c0 fs/namei.c:2004
>  link_path_walk.part.0+0x773/0xda0 fs/namei.c:2331
>  link_path_walk fs/namei.c:3826 [inline]
>  path_openat+0x1b9/0x520 fs/namei.c:3826
>  do_filp_open+0x1b7/0x400 fs/namei.c:3857
>  do_sys_openat2+0x5dc/0x6e0 fs/open.c:1428
>  do_sys_open fs/open.c:1443 [inline]
>  __do_sys_openat fs/open.c:1459 [inline]
>  __se_sys_openat fs/open.c:1454 [inline]
>  __x64_sys_openat+0x148/0x200 fs/open.c:1454
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
>  entry_SYSCALL_64_after_hwframe+0x78/0xe2
> 
> Freed by task 232726:
>  kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
>  kasan_set_track+0x25/0x30 mm/kasan/common.c:52
>  kasan_save_free_info+0x2b/0x50 mm/kasan/generic.c:522
>  ____kasan_slab_free mm/kasan/common.c:236 [inline]
>  __kasan_slab_free+0x12a/0x1b0 mm/kasan/common.c:244
>  kasan_slab_free include/linux/kasan.h:164 [inline]
>  slab_free_hook mm/slub.c:1827 [inline]
>  slab_free_freelist_hook mm/slub.c:1853 [inline]
>  slab_free mm/slub.c:3820 [inline]
>  kmem_cache_free+0x110/0x760 mm/slub.c:3842
>  bfq_put_queue+0x6a7/0xfb0 block/bfq-iosched.c:5428
>  bfq_forget_entity block/bfq-wf2q.c:634 [inline]
>  bfq_put_idle_entity+0x142/0x240 block/bfq-wf2q.c:645
>  bfq_forget_idle+0x189/0x1e0 block/bfq-wf2q.c:671
>  bfq_update_vtime block/bfq-wf2q.c:1280 [inline]
>  __bfq_lookup_next_entity block/bfq-wf2q.c:1374 [inline]
>  bfq_lookup_next_entity+0x350/0x480 block/bfq-wf2q.c:1433
>  bfq_update_next_in_service+0x1c0/0x4f0 block/bfq-wf2q.c:128
>  bfq_deactivate_entity+0x10a/0x240 block/bfq-wf2q.c:1188
>  bfq_deactivate_bfqq block/bfq-wf2q.c:1592 [inline]
>  bfq_del_bfqq_busy+0x2e8/0xad0 block/bfq-wf2q.c:1659
>  bfq_release_process_ref+0x1cc/0x220 block/bfq-iosched.c:3139
>  bfq_split_bfqq+0x481/0xdf0 block/bfq-iosched.c:6754
>  bfq_init_rq+0xf29/0x17a0 block/bfq-iosched.c:6934
>  bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
>  bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
>  blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
>  blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
>  __submit_bio+0xa0/0x6b0 block/blk-core.c:639
>  __submit_bio_noacct_mq block/blk-core.c:718 [inline]
>  submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
>  submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
>  __ext4_read_bh fs/ext4/super.c:205 [inline]
>  ext4_read_bh+0x15e/0x2e0 fs/ext4/super.c:230
>  __read_extent_tree_block+0x304/0x6f0 fs/ext4/extents.c:567
>  ext4_find_extent+0x479/0xd20 fs/ext4/extents.c:947
>  ext4_ext_map_blocks+0x1a3/0x2680 fs/ext4/extents.c:4182
>  ext4_map_blocks+0x929/0x15a0 fs/ext4/inode.c:660
>  ext4_iomap_begin_report+0x298/0x480 fs/ext4/inode.c:3569
>  iomap_iter+0x3dd/0x1010 fs/iomap/iter.c:91
>  iomap_fiemap+0x1f4/0x360 fs/iomap/fiemap.c:80
>  ext4_fiemap+0x181/0x210 fs/ext4/extents.c:5051
>  ioctl_fiemap.isra.0+0x1b4/0x290 fs/ioctl.c:220
>  do_vfs_ioctl+0x31c/0x11a0 fs/ioctl.c:811
>  __do_sys_ioctl fs/ioctl.c:869 [inline]
>  __se_sys_ioctl+0xae/0x190 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
>  entry_SYSCALL_64_after_hwframe+0x78/0xe2
> 
> commit 1ba0403ac644 ("block, bfq: fix uaf for accessing waker_bfqq after
> splitting") fix the problem that if waker_bfqq is in the merge chain,
> and current is the only procress, waker_bfqq can be freed from
> bfq_split_bfqq(). However, the case that waker_bfqq is not in the merge
> chain is missed, and if the procress reference of waker_bfqq is 0,
> waker_bfqq can be freed as well.
> 
> Fix the problem by checking procress reference if waker_bfqq is not in
> the merge_chain.
> 
> Fixes: 1ba0403ac644 ("block, bfq: fix uaf for accessing waker_bfqq after splitting")
> Signed-off-by: Hou Tao <houtao1@huawei.com>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  block/bfq-iosched.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 068c63e95738..c69e9faad15a 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -6844,16 +6844,24 @@ static struct bfq_queue *bfq_waker_bfqq(struct bfq_queue *bfqq)
>  		if (new_bfqq == waker_bfqq) {
>  			/*
>  			 * If waker_bfqq is in the merge chain, and current
> -			 * is the only procress.
> +			 * is the only procress, waker_bfqq can be freed.
					^^^ can you please fix the typo
while modifying the comment? It should be "process".


>  			 */
>  			if (bfqq_process_refs(waker_bfqq) == 1)
>  				return NULL;
> -			break;
> +
> +			return waker_bfqq;

So how do you know bfqq_process_refs(waker_bfqq) is not 0 in this case?

>  		}
>  
>  		new_bfqq = new_bfqq->new_bfqq;
>  	}
>  
> +	/*
> +	 * If waker_bfqq is not in the merge chain, and it's procress reference
							     ^^^ process
> +	 * is 0, waker_bfqq can be freed.
> +	 */
> +	if (bfqq_process_refs(waker_bfqq) == 0)
> +		return NULL;
> +
>  	return waker_bfqq;
>  }

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR
Re: [PATCH] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()
Posted by Yu Kuai 11 months, 2 weeks ago 
Hi,

在 2025/01/08 22:42, Jan Kara 写道:
> On Wed 08-01-25 16:41:48, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> Our syzkaller report a following UAF for v6.6:
>>
>> BUG: KASAN: slab-use-after-free in bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958
>> Read of size 8 at addr ffff8881b57147d8 by task fsstress/232726
>>
>> CPU: 2 PID: 232726 Comm: fsstress Not tainted 6.6.0-g3629d1885222 #39
>> Call Trace:
>>   <TASK>
>>   __dump_stack lib/dump_stack.c:88 [inline]
>>   dump_stack_lvl+0x91/0xf0 lib/dump_stack.c:106
>>   print_address_description.constprop.0+0x66/0x300 mm/kasan/report.c:364
>>   print_report+0x3e/0x70 mm/kasan/report.c:475
>>   kasan_report+0xb8/0xf0 mm/kasan/report.c:588
>>   hlist_add_head include/linux/list.h:1023 [inline]
>>   bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958
>>   bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
>>   bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
>>   blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
>>   blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
>>   __submit_bio+0xa0/0x6b0 block/blk-core.c:639
>>   __submit_bio_noacct_mq block/blk-core.c:718 [inline]
>>   submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
>>   submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
>>   __ext4_read_bh fs/ext4/super.c:205 [inline]
>>   ext4_read_bh+0x15e/0x2e0 fs/ext4/super.c:230
>>   __read_extent_tree_block+0x304/0x6f0 fs/ext4/extents.c:567
>>   ext4_find_extent+0x479/0xd20 fs/ext4/extents.c:947
>>   ext4_ext_map_blocks+0x1a3/0x2680 fs/ext4/extents.c:4182
>>   ext4_map_blocks+0x929/0x15a0 fs/ext4/inode.c:660
>>   ext4_iomap_begin_report+0x298/0x480 fs/ext4/inode.c:3569
>>   iomap_iter+0x3dd/0x1010 fs/iomap/iter.c:91
>>   iomap_fiemap+0x1f4/0x360 fs/iomap/fiemap.c:80
>>   ext4_fiemap+0x181/0x210 fs/ext4/extents.c:5051
>>   ioctl_fiemap.isra.0+0x1b4/0x290 fs/ioctl.c:220
>>   do_vfs_ioctl+0x31c/0x11a0 fs/ioctl.c:811
>>   __do_sys_ioctl fs/ioctl.c:869 [inline]
>>   __se_sys_ioctl+0xae/0x190 fs/ioctl.c:857
>>   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>>   do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
>>   entry_SYSCALL_64_after_hwframe+0x78/0xe2
>>
>> Allocated by task 232719:
>>   kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
>>   kasan_set_track+0x25/0x30 mm/kasan/common.c:52
>>   __kasan_slab_alloc+0x87/0x90 mm/kasan/common.c:328
>>   kasan_slab_alloc include/linux/kasan.h:188 [inline]
>>   slab_post_alloc_hook mm/slab.h:768 [inline]
>>   slab_alloc_node mm/slub.c:3492 [inline]
>>   kmem_cache_alloc_node+0x1b8/0x6f0 mm/slub.c:3537
>>   bfq_get_queue+0x215/0x1f00 block/bfq-iosched.c:5869
>>   bfq_get_bfqq_handle_split+0x167/0x5f0 block/bfq-iosched.c:6776
>>   bfq_init_rq+0x13a4/0x17a0 block/bfq-iosched.c:6938
>>   bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
>>   bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
>>   blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
>>   blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
>>   __submit_bio+0xa0/0x6b0 block/blk-core.c:639
>>   __submit_bio_noacct_mq block/blk-core.c:718 [inline]
>>   submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
>>   submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
>>   __ext4_read_bh fs/ext4/super.c:205 [inline]
>>   ext4_read_bh_nowait+0x15a/0x240 fs/ext4/super.c:217
>>   ext4_read_bh_lock+0xac/0xd0 fs/ext4/super.c:242
>>   ext4_bread_batch+0x268/0x500 fs/ext4/inode.c:958
>>   __ext4_find_entry+0x448/0x10f0 fs/ext4/namei.c:1671
>>   ext4_lookup_entry fs/ext4/namei.c:1774 [inline]
>>   ext4_lookup.part.0+0x359/0x6f0 fs/ext4/namei.c:1842
>>   ext4_lookup+0x72/0x90 fs/ext4/namei.c:1839
>>   __lookup_slow+0x257/0x480 fs/namei.c:1696
>>   lookup_slow fs/namei.c:1713 [inline]
>>   walk_component+0x454/0x5c0 fs/namei.c:2004
>>   link_path_walk.part.0+0x773/0xda0 fs/namei.c:2331
>>   link_path_walk fs/namei.c:3826 [inline]
>>   path_openat+0x1b9/0x520 fs/namei.c:3826
>>   do_filp_open+0x1b7/0x400 fs/namei.c:3857
>>   do_sys_openat2+0x5dc/0x6e0 fs/open.c:1428
>>   do_sys_open fs/open.c:1443 [inline]
>>   __do_sys_openat fs/open.c:1459 [inline]
>>   __se_sys_openat fs/open.c:1454 [inline]
>>   __x64_sys_openat+0x148/0x200 fs/open.c:1454
>>   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>>   do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
>>   entry_SYSCALL_64_after_hwframe+0x78/0xe2
>>
>> Freed by task 232726:
>>   kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
>>   kasan_set_track+0x25/0x30 mm/kasan/common.c:52
>>   kasan_save_free_info+0x2b/0x50 mm/kasan/generic.c:522
>>   ____kasan_slab_free mm/kasan/common.c:236 [inline]
>>   __kasan_slab_free+0x12a/0x1b0 mm/kasan/common.c:244
>>   kasan_slab_free include/linux/kasan.h:164 [inline]
>>   slab_free_hook mm/slub.c:1827 [inline]
>>   slab_free_freelist_hook mm/slub.c:1853 [inline]
>>   slab_free mm/slub.c:3820 [inline]
>>   kmem_cache_free+0x110/0x760 mm/slub.c:3842
>>   bfq_put_queue+0x6a7/0xfb0 block/bfq-iosched.c:5428
>>   bfq_forget_entity block/bfq-wf2q.c:634 [inline]
>>   bfq_put_idle_entity+0x142/0x240 block/bfq-wf2q.c:645
>>   bfq_forget_idle+0x189/0x1e0 block/bfq-wf2q.c:671
>>   bfq_update_vtime block/bfq-wf2q.c:1280 [inline]
>>   __bfq_lookup_next_entity block/bfq-wf2q.c:1374 [inline]
>>   bfq_lookup_next_entity+0x350/0x480 block/bfq-wf2q.c:1433
>>   bfq_update_next_in_service+0x1c0/0x4f0 block/bfq-wf2q.c:128
>>   bfq_deactivate_entity+0x10a/0x240 block/bfq-wf2q.c:1188
>>   bfq_deactivate_bfqq block/bfq-wf2q.c:1592 [inline]
>>   bfq_del_bfqq_busy+0x2e8/0xad0 block/bfq-wf2q.c:1659
>>   bfq_release_process_ref+0x1cc/0x220 block/bfq-iosched.c:3139
>>   bfq_split_bfqq+0x481/0xdf0 block/bfq-iosched.c:6754
>>   bfq_init_rq+0xf29/0x17a0 block/bfq-iosched.c:6934
>>   bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
>>   bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
>>   blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
>>   blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
>>   __submit_bio+0xa0/0x6b0 block/blk-core.c:639
>>   __submit_bio_noacct_mq block/blk-core.c:718 [inline]
>>   submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
>>   submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
>>   __ext4_read_bh fs/ext4/super.c:205 [inline]
>>   ext4_read_bh+0x15e/0x2e0 fs/ext4/super.c:230
>>   __read_extent_tree_block+0x304/0x6f0 fs/ext4/extents.c:567
>>   ext4_find_extent+0x479/0xd20 fs/ext4/extents.c:947
>>   ext4_ext_map_blocks+0x1a3/0x2680 fs/ext4/extents.c:4182
>>   ext4_map_blocks+0x929/0x15a0 fs/ext4/inode.c:660
>>   ext4_iomap_begin_report+0x298/0x480 fs/ext4/inode.c:3569
>>   iomap_iter+0x3dd/0x1010 fs/iomap/iter.c:91
>>   iomap_fiemap+0x1f4/0x360 fs/iomap/fiemap.c:80
>>   ext4_fiemap+0x181/0x210 fs/ext4/extents.c:5051
>>   ioctl_fiemap.isra.0+0x1b4/0x290 fs/ioctl.c:220
>>   do_vfs_ioctl+0x31c/0x11a0 fs/ioctl.c:811
>>   __do_sys_ioctl fs/ioctl.c:869 [inline]
>>   __se_sys_ioctl+0xae/0x190 fs/ioctl.c:857
>>   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>>   do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
>>   entry_SYSCALL_64_after_hwframe+0x78/0xe2
>>
>> commit 1ba0403ac644 ("block, bfq: fix uaf for accessing waker_bfqq after
>> splitting") fix the problem that if waker_bfqq is in the merge chain,
>> and current is the only procress, waker_bfqq can be freed from
>> bfq_split_bfqq(). However, the case that waker_bfqq is not in the merge
>> chain is missed, and if the procress reference of waker_bfqq is 0,
>> waker_bfqq can be freed as well.
>>
>> Fix the problem by checking procress reference if waker_bfqq is not in
>> the merge_chain.
>>
>> Fixes: 1ba0403ac644 ("block, bfq: fix uaf for accessing waker_bfqq after splitting")
>> Signed-off-by: Hou Tao <houtao1@huawei.com>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   block/bfq-iosched.c | 12 ++++++++++--
>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
>> index 068c63e95738..c69e9faad15a 100644
>> --- a/block/bfq-iosched.c
>> +++ b/block/bfq-iosched.c
>> @@ -6844,16 +6844,24 @@ static struct bfq_queue *bfq_waker_bfqq(struct bfq_queue *bfqq)
>>   		if (new_bfqq == waker_bfqq) {
>>   			/*
>>   			 * If waker_bfqq is in the merge chain, and current
>> -			 * is the only procress.
>> +			 * is the only procress, waker_bfqq can be freed.
> 					^^^ can you please fix the typo
> while modifying the comment? It should be "process".

Sorry for the typo, I didn't notice it at all. :(
> 
> 
>>   			 */
>>   			if (bfqq_process_refs(waker_bfqq) == 1)
>>   				return NULL;
>> -			break;
>> +
>> +			return waker_bfqq;
> 
> So how do you know bfqq_process_refs(waker_bfqq) is not 0 in this case?

Because in this case, waker_bfqq is in the merge chain of bfqq, and bfqq
is obtained frm the current process, which means waker_bfqq should have
at least one process reference that is from current thread.

Thanks,
Kuai

> 
>>   		}
>>   
>>   		new_bfqq = new_bfqq->new_bfqq;
>>   	}
>>   
>> +	/*
>> +	 * If waker_bfqq is not in the merge chain, and it's procress reference
> 							     ^^^ process
>> +	 * is 0, waker_bfqq can be freed.
>> +	 */
>> +	if (bfqq_process_refs(waker_bfqq) == 0)
>> +		return NULL;
>> +
>>   	return waker_bfqq;
>>   }
> 
> 								Honza
>
Re: [PATCH] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()
Posted by Jan Kara 11 months, 2 weeks ago 
On Thu 09-01-25 09:32:08, Yu Kuai wrote:
> Hi,
> 
> 在 2025/01/08 22:42, Jan Kara 写道:
> > 
> > 
> > >   			 */
> > >   			if (bfqq_process_refs(waker_bfqq) == 1)
> > >   				return NULL;
> > > -			break;
> > > +
> > > +			return waker_bfqq;
> > 
> > So how do you know bfqq_process_refs(waker_bfqq) is not 0 in this case?
> 
> Because in this case, waker_bfqq is in the merge chain of bfqq, and bfqq
> is obtained frm the current process, which means waker_bfqq should have
> at least one process reference that is from current thread.

Ah, right. Thanks for explanation. The except for the typo the patch looks
good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

(although I can see Jens has already picked up the patch so probably this
is immaterial).

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR
Re: [PATCH] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()
Posted by Jens Axboe 11 months, 2 weeks ago 
On 1/9/25 1:50 AM, Jan Kara wrote:
> On Thu 09-01-25 09:32:08, Yu Kuai wrote:
>> Hi,
>>
>> ? 2025/01/08 22:42, Jan Kara ??:
>>>
>>>
>>>>   			 */
>>>>   			if (bfqq_process_refs(waker_bfqq) == 1)
>>>>   				return NULL;
>>>> -			break;
>>>> +
>>>> +			return waker_bfqq;
>>>
>>> So how do you know bfqq_process_refs(waker_bfqq) is not 0 in this case?
>>
>> Because in this case, waker_bfqq is in the merge chain of bfqq, and bfqq
>> is obtained frm the current process, which means waker_bfqq should have
>> at least one process reference that is from current thread.
> 
> Ah, right. Thanks for explanation. The except for the typo the patch looks
> good to me. Feel free to add:
> 
> Reviewed-by: Jan Kara <jack@suse.cz>
> 
> (although I can see Jens has already picked up the patch so probably this
> is immaterial).

Still useful! The patch has a link to this thread, so it's still
connected even if the commit itself isn't updated. Though with the typo
in process, I'm kind of pondering just amending the commit and then I'll
add your reviewed-by as well. But usually I don't, but still appreciate
reviews after it's been queued.

-- 
Jens Axboe
Re: [PATCH] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()
Posted by Jens Axboe 11 months, 2 weeks ago 
On Wed, 08 Jan 2025 16:41:48 +0800, Yu Kuai wrote:
> Our syzkaller report a following UAF for v6.6:
> 
> BUG: KASAN: slab-use-after-free in bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958
> Read of size 8 at addr ffff8881b57147d8 by task fsstress/232726
> 
> CPU: 2 PID: 232726 Comm: fsstress Not tainted 6.6.0-g3629d1885222 #39
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x91/0xf0 lib/dump_stack.c:106
>  print_address_description.constprop.0+0x66/0x300 mm/kasan/report.c:364
>  print_report+0x3e/0x70 mm/kasan/report.c:475
>  kasan_report+0xb8/0xf0 mm/kasan/report.c:588
>  hlist_add_head include/linux/list.h:1023 [inline]
>  bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958
>  bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271
>  bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323
>  blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660
>  blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143
>  __submit_bio+0xa0/0x6b0 block/blk-core.c:639
>  __submit_bio_noacct_mq block/blk-core.c:718 [inline]
>  submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747
>  submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847
>  __ext4_read_bh fs/ext4/super.c:205 [inline]
>  ext4_read_bh+0x15e/0x2e0 fs/ext4/super.c:230
>  __read_extent_tree_block+0x304/0x6f0 fs/ext4/extents.c:567
>  ext4_find_extent+0x479/0xd20 fs/ext4/extents.c:947
>  ext4_ext_map_blocks+0x1a3/0x2680 fs/ext4/extents.c:4182
>  ext4_map_blocks+0x929/0x15a0 fs/ext4/inode.c:660
>  ext4_iomap_begin_report+0x298/0x480 fs/ext4/inode.c:3569
>  iomap_iter+0x3dd/0x1010 fs/iomap/iter.c:91
>  iomap_fiemap+0x1f4/0x360 fs/iomap/fiemap.c:80
>  ext4_fiemap+0x181/0x210 fs/ext4/extents.c:5051
>  ioctl_fiemap.isra.0+0x1b4/0x290 fs/ioctl.c:220
>  do_vfs_ioctl+0x31c/0x11a0 fs/ioctl.c:811
>  __do_sys_ioctl fs/ioctl.c:869 [inline]
>  __se_sys_ioctl+0xae/0x190 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
>  entry_SYSCALL_64_after_hwframe+0x78/0xe2
> 
> [...]

Applied, thanks!

[1/1] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()
      commit: eb92f7314625807ad569c218039ec90e9e14c784

Best regards,
-- 
Jens Axboe

Patchew 2.1-devel-b67e4c2

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