fs/exfat/dir.c | 111 +++++++++----------------------------------- fs/exfat/exfat_fs.h | 49 ++++++++++++++++++- fs/exfat/fatent.c | 23 ++++----- fs/exfat/inode.c | 11 +---- fs/exfat/namei.c | 29 +++--------- 5 files changed, 88 insertions(+), 135 deletions(-)
From: Chi Zhiling <chizhiling@kylinos.cn> This series introduces and uses two new helpers to simplify FAT chain walking logic across the exfat driver: 1. exfat_fat_walk - walks FAT chain by a given step, handling both ALLOC_NO_FAT_CHAIN and ALLOC_FAT_CHAIN modes 2. exfat_chain_advance - walks an exfat_chain structure by a given step, updating both ->dir and ->size fields atomically with proper boundary checking These helpers replace open-coded cluster walking logic in dir.c, namei.c and inode.c, improving code readability and ensuring consistent error handling for corrupted FAT chains. Also includes a fix for incorrect directory checksum when renaming a file to a shorter name. The base commit is exfat/dev without iomap changes Chi Zhiling (6): exfat: fix incorrect directory checksum after rename to shorter name exfat: introduce exfat_fat_walk helper exfat: use exfat_fat_walk helper to simplify fat entry walking exfat: remove NULL cache pointer case in exfat_ent_get exfat: introduce exfat_chain_advance helper exfat: use exfat_chain_advance helper fs/exfat/dir.c | 111 +++++++++----------------------------------- fs/exfat/exfat_fs.h | 49 ++++++++++++++++++- fs/exfat/fatent.c | 23 ++++----- fs/exfat/inode.c | 11 +---- fs/exfat/namei.c | 29 +++--------- 5 files changed, 88 insertions(+), 135 deletions(-) -- 2.43.0
syzbot ci has tested the following series [v1] exfat: unify FAT chain walking helpers https://lore.kernel.org/all/20260331091113.20882-1-chizhiling@163.com * [PATCH v1 1/6] exfat: fix incorrect directory checksum after rename to shorter name * [PATCH v1 2/6] exfat: introduce exfat_fat_walk helper * [PATCH v1 3/6] exfat: use exfat_fat_walk helper to simplify fat entry walking * [PATCH v1 4/6] exfat: remove NULL cache pointer case in exfat_ent_get * [PATCH v1 5/6] exfat: introduce exfat_chain_advance helper * [PATCH v1 6/6] exfat: use exfat_chain_advance helper and found the following issue: WARNING in exfat_find_empty_entry Full report is available here: https://ci.syzbot.org/series/d9d5a999-e11a-43e1-ac76-9c718e136f25 *** WARNING in exfat_find_empty_entry tree: linux-next URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next base: d1d75eaf01abceb3d5cb50253375b5f254b6be54 arch: amd64 compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 config: https://ci.syzbot.org/builds/177ab8e9-7eef-44cc-8b1d-6e8e2b44adaf/config C repro: https://ci.syzbot.org/findings/9b0e35b9-b5be-440e-9461-2f19c03cb16a/c_repro syz repro: https://ci.syzbot.org/findings/9b0e35b9-b5be-440e-9461-2f19c03cb16a/syz_repro exFAT-fs (loop0): start_clu is invalid cluster(0xffffffff) exFAT-fs (loop0): valid_size(150994954) is greater than size(10) ------------[ cut here ]------------ chain->dir != EXFAT_EOF_CLUSTER WARNING: fs/exfat/exfat_fs.h:575 at exfat_chain_advance fs/exfat/exfat_fs.h:575 [inline], CPU#0: syz.0.17/5981 WARNING: fs/exfat/exfat_fs.h:575 at exfat_search_empty_slot fs/exfat/namei.c:249 [inline], CPU#0: syz.0.17/5981 WARNING: fs/exfat/exfat_fs.h:575 at exfat_find_empty_entry+0x754/0x13b0 fs/exfat/namei.c:318, CPU#0: syz.0.17/5981 Modules linked in: CPU: 0 UID: 0 PID: 5981 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 RIP: 0010:exfat_chain_advance fs/exfat/exfat_fs.h:575 [inline] RIP: 0010:exfat_search_empty_slot fs/exfat/namei.c:249 [inline] RIP: 0010:exfat_find_empty_entry+0x754/0x13b0 fs/exfat/namei.c:318 Code: 00 bf ff ff ff ff 44 89 e6 e8 18 56 1f ff 41 83 fc ff 75 10 e8 cd 51 1f ff 45 29 ee 0f 8d ad fe ff ff eb 12 e8 bd 51 1f ff 90 <0f> 0b 90 45 29 ee 0f 8d 99 fe ff ff e8 ab 51 1f ff 41 01 df 48 8b RSP: 0018:ffffc9000499f340 EFLAGS: 00010293 RAX: ffffffff82a639c3 RBX: 0000000000000020 RCX: ffff88816d588000 RDX: 0000000000000000 RSI: 000000000000000b RDI: 00000000ffffffff RBP: ffffc9000499f570 R08: ffff888119e14a5b R09: 1ffff110233c294b R10: dffffc0000000000 R11: ffffed10233c294c R12: 000000000000000b R13: 0000000000000080 R14: 0000000000000000 R15: 0000000000000060 FS: 000055557e214500(0000) GS:ffff88818de66000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000006200 CR3: 00000001bcf7c000 CR4: 00000000000006f0 Call Trace: <TASK> exfat_rename_file fs/exfat/namei.c:1025 [inline] __exfat_rename fs/exfat/namei.c:1177 [inline] exfat_rename+0xb49/0x1f90 fs/exfat/namei.c:1251 vfs_rename+0xa96/0xeb0 fs/namei.c:6026 filename_renameat2+0x539/0x9c0 fs/namei.c:6144 __do_sys_rename fs/namei.c:6188 [inline] __se_sys_rename+0x55/0x2c0 fs/namei.c:6184 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f66f1b9c819 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffcad04e2e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000052 RAX: ffffffffffffffda RBX: 00007f66f1e15fa0 RCX: 00007f66f1b9c819 RDX: 0000000000000000 RSI: 0000200000000400 RDI: 0000200000006200 RBP: 00007f66f1c32c91 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f66f1e15fac R14: 00007f66f1e15fa0 R15: 00007f66f1e15fa0 </TASK> *** If these findings have caused you to resend the series or submit a separate fix, please add the following tag to your commit message: Tested-by: syzbot@syzkaller.appspotmail.com --- This report is generated by a bot. It may contain errors. syzbot ci engineers can be reached at syzkaller@googlegroups.com. To test a patch for this bug, please reply with `#syz test` (should be on a separate line). The patch should be attached to the email. Note: arguments like custom git repos and branches are not supported.
On 3/31/26 11:27 PM, syzbot ci wrote: > syzbot ci has tested the following series > > [v1] exfat: unify FAT chain walking helpers > https://lore.kernel.org/all/20260331091113.20882-1-chizhiling@163.com > * [PATCH v1 1/6] exfat: fix incorrect directory checksum after rename to shorter name > * [PATCH v1 2/6] exfat: introduce exfat_fat_walk helper > * [PATCH v1 3/6] exfat: use exfat_fat_walk helper to simplify fat entry walking > * [PATCH v1 4/6] exfat: remove NULL cache pointer case in exfat_ent_get > * [PATCH v1 5/6] exfat: introduce exfat_chain_advance helper > * [PATCH v1 6/6] exfat: use exfat_chain_advance helper > > and found the following issue: > WARNING in exfat_find_empty_entry > > Full report is available here: > https://ci.syzbot.org/series/d9d5a999-e11a-43e1-ac76-9c718e136f25 > > *** > > WARNING in exfat_find_empty_entry > > tree: linux-next > URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next > base: d1d75eaf01abceb3d5cb50253375b5f254b6be54 > arch: amd64 > compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 > config: https://ci.syzbot.org/builds/177ab8e9-7eef-44cc-8b1d-6e8e2b44adaf/config > C repro: https://ci.syzbot.org/findings/9b0e35b9-b5be-440e-9461-2f19c03cb16a/c_repro > syz repro: https://ci.syzbot.org/findings/9b0e35b9-b5be-440e-9461-2f19c03cb16a/syz_repro > > exFAT-fs (loop0): start_clu is invalid cluster(0xffffffff) > exFAT-fs (loop0): valid_size(150994954) is greater than size(10) > ------------[ cut here ]------------ > chain->dir != EXFAT_EOF_CLUSTER > WARNING: fs/exfat/exfat_fs.h:575 at exfat_chain_advance fs/exfat/exfat_fs.h:575 [inline], CPU#0: syz.0.17/5981 > WARNING: fs/exfat/exfat_fs.h:575 at exfat_search_empty_slot fs/exfat/namei.c:249 [inline], CPU#0: syz.0.17/5981 > WARNING: fs/exfat/exfat_fs.h:575 at exfat_find_empty_entry+0x754/0x13b0 fs/exfat/namei.c:318, CPU#0: syz.0.17/5981 > Modules linked in: > CPU: 0 UID: 0 PID: 5981 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 > RIP: 0010:exfat_chain_advance fs/exfat/exfat_fs.h:575 [inline] > RIP: 0010:exfat_search_empty_slot fs/exfat/namei.c:249 [inline] > RIP: 0010:exfat_find_empty_entry+0x754/0x13b0 fs/exfat/namei.c:318 > Code: 00 bf ff ff ff ff 44 89 e6 e8 18 56 1f ff 41 83 fc ff 75 10 e8 cd 51 1f ff 45 29 ee 0f 8d ad fe ff ff eb 12 e8 bd 51 1f ff 90 <0f> 0b 90 45 29 ee 0f 8d 99 fe ff ff e8 ab 51 1f ff 41 01 df 48 8b > RSP: 0018:ffffc9000499f340 EFLAGS: 00010293 > RAX: ffffffff82a639c3 RBX: 0000000000000020 RCX: ffff88816d588000 > RDX: 0000000000000000 RSI: 000000000000000b RDI: 00000000ffffffff > RBP: ffffc9000499f570 R08: ffff888119e14a5b R09: 1ffff110233c294b > R10: dffffc0000000000 R11: ffffed10233c294c R12: 000000000000000b > R13: 0000000000000080 R14: 0000000000000000 R15: 0000000000000060 > FS: 000055557e214500(0000) GS:ffff88818de66000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000200000006200 CR3: 00000001bcf7c000 CR4: 00000000000006f0 > Call Trace: > <TASK> > exfat_rename_file fs/exfat/namei.c:1025 [inline] > __exfat_rename fs/exfat/namei.c:1177 [inline] > exfat_rename+0xb49/0x1f90 fs/exfat/namei.c:1251 > vfs_rename+0xa96/0xeb0 fs/namei.c:6026 > filename_renameat2+0x539/0x9c0 fs/namei.c:6144 > __do_sys_rename fs/namei.c:6188 [inline] > __se_sys_rename+0x55/0x2c0 fs/namei.c:6184 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7f66f1b9c819 > Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007ffcad04e2e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000052 > RAX: ffffffffffffffda RBX: 00007f66f1e15fa0 RCX: 00007f66f1b9c819 > RDX: 0000000000000000 RSI: 0000200000000400 RDI: 0000200000006200 > RBP: 00007f66f1c32c91 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > R13: 00007f66f1e15fac R14: 00007f66f1e15fa0 R15: 00007f66f1e15fa0 > </TASK> It looks like I should remove this WARN_ON_ONCE statement. This check is not reasonable when accessing directories, and I will fix it in v2. Thanks, > > > *** > > If these findings have caused you to resend the series or submit a > separate fix, please add the following tag to your commit message: > Tested-by: syzbot@syzkaller.appspotmail.com > > --- > This report is generated by a bot. It may contain errors. > syzbot ci engineers can be reached at syzkaller@googlegroups.com. > > To test a patch for this bug, please reply with `#syz test` > (should be on a separate line). > > The patch should be attached to the email. > Note: arguments like custom git repos and branches are not supported.
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