#syz test
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 3615c06b7dfa..1389712bc1df 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -42,6 +42,28 @@ static inline int stack_map_data_size(struct bpf_map *map)
sizeof(struct bpf_stack_build_id) : sizeof(u64);
}
+/**
+ * stack_map_calculate_max_depth - Calculate maximum allowed stack trace depth
+ * @size: Size of the buffer/map value in bytes
+ * @elem_size: Size of each stack trace element
+ * @flags: BPF stack trace flags (BPF_F_USER_STACK, BPF_F_USER_BUILD_ID, ...)
+ *
+ * Return: Maximum number of stack trace entries that can be safely stored
+ */
+static u32 stack_map_calculate_max_depth(u32 size, u32 elem_size, u64 flags)
+{
+ u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
+ u32 max_depth;
+ u32 curr_sysctl_max_stack = READ_ONCE(sysctl_perf_event_max_stack);
+
+ max_depth = size / elem_size;
+ max_depth += skip;
+ if (max_depth > curr_sysctl_max_stack)
+ return curr_sysctl_max_stack;
+
+ return max_depth;
+}
+
static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
{
u64 elem_size = sizeof(struct stack_map_bucket) +
@@ -300,22 +322,20 @@ static long __bpf_get_stackid(struct bpf_map *map,
BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
u64, flags)
{
- u32 max_depth = map->value_size / stack_map_data_size(map);
- u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
+ u32 elem_size = stack_map_data_size(map);
bool user = flags & BPF_F_USER_STACK;
struct perf_callchain_entry *trace;
bool kernel = !user;
+ u32 max_depth;
if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
return -EINVAL;
- max_depth += skip;
- if (max_depth > sysctl_perf_event_max_stack)
- max_depth = sysctl_perf_event_max_stack;
-
+ max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags);
trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
false, false);
+ trace->nr = min_t(u32, trace->nr, max_depth);
if (unlikely(!trace))
/* couldn't fetch the stack trace */
@@ -350,6 +370,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
{
struct perf_event *event = ctx->event;
struct perf_callchain_entry *trace;
+ u32 elem_size, max_depth;
bool kernel, user;
__u64 nr_kernel;
int ret;
@@ -371,11 +392,15 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
return -EFAULT;
nr_kernel = count_kernel_ip(trace);
+ elem_size = stack_map_data_size(map);
if (kernel) {
__u64 nr = trace->nr;
trace->nr = nr_kernel;
+ max_depth =
+ stack_map_calculate_max_depth(map->value_size, elem_size, flags);
+ trace->nr = min_t(u32, nr_kernel, max_depth);
ret = __bpf_get_stackid(map, trace, flags);
/* restore nr */
@@ -388,6 +413,9 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
return -EFAULT;
flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
+ max_depth =
+ stack_map_calculate_max_depth(map->value_size, elem_size, flags);
+ trace->nr = min_t(u32, trace->nr, max_depth);
ret = __bpf_get_stackid(map, trace, flags);
}
return ret;
@@ -406,8 +434,8 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
struct perf_callchain_entry *trace_in,
void *buf, u32 size, u64 flags, bool may_fault)
{
- u32 trace_nr, copy_len, elem_size, num_elem, max_depth;
bool user_build_id = flags & BPF_F_USER_BUILD_ID;
+ u32 trace_nr, copy_len, elem_size, max_depth;
bool crosstask = task && task != current;
u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
bool user = flags & BPF_F_USER_STACK;
@@ -438,21 +466,20 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
goto clear;
}
- num_elem = size / elem_size;
- max_depth = num_elem + skip;
- if (sysctl_perf_event_max_stack < max_depth)
- max_depth = sysctl_perf_event_max_stack;
+ max_depth = stack_map_calculate_max_depth(size, elem_size, flags);
if (may_fault)
rcu_read_lock(); /* need RCU for perf's callchain below */
- if (trace_in)
+ if (trace_in) {
trace = trace_in;
- else if (kernel && task)
+ trace->nr = min_t(u32, trace->nr, max_depth);
+ } else if (kernel && task) {
trace = get_callchain_entry_for_task(task, max_depth);
- else
+ } else {
trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
crosstask, false);
+ }
if (unlikely(!trace) || trace->nr < skip) {
if (may_fault)
@@ -461,7 +488,6 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
}
trace_nr = trace->nr - skip;
- trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem;
copy_len = trace_nr * elem_size;
ips = trace->ip + skip;
--
2.47.3On Thu, 4 Sep 2025 16:11:13 +0200 Arnaud Lecomte wrote: > #syz test You are hereby encouraged to not CC the vger MLs on your attempts to get your patches tested by syzbot. It's not necessary.
On 04/09/2025 16:47, Jakub Kicinski wrote: > On Thu, 4 Sep 2025 16:11:13 +0200 Arnaud Lecomte wrote: >> #syz test > You are hereby encouraged to not CC the vger MLs on your attempts > to get your patches tested by syzbot. It's not necessary. > Hey, sorry for the inconvenience. Will be removed.
Hello,
syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-out-of-bounds Write in __bpf_get_stackid
==================================================================
BUG: KASAN: slab-out-of-bounds in __bpf_get_stackid+0x677/0xcf0 kernel/bpf/stackmap.c:287
Write of size 8 at addr ffff88802fd43258 by task syz.3.65/6980
CPU: 1 UID: 0 PID: 6980 Comm: syz.3.65 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
<IRQ>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
__bpf_get_stackid+0x677/0xcf0 kernel/bpf/stackmap.c:287
____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1810 [inline]
bpf_get_stackid_raw_tp+0x196/0x210 kernel/trace/bpf_trace.c:1799
bpf_prog_b724608cae728045+0x27/0x2f
bpf_dispatcher_nop_func include/linux/bpf.h:1332 [inline]
__bpf_prog_run include/linux/filter.h:718 [inline]
bpf_prog_run include/linux/filter.h:725 [inline]
__bpf_trace_run kernel/trace/bpf_trace.c:2257 [inline]
bpf_trace_run2+0x281/0x4b0 kernel/trace/bpf_trace.c:2298
__do_trace_kfree include/trace/events/kmem.h:94 [inline]
trace_kfree include/trace/events/kmem.h:94 [inline]
kfree+0x3a0/0x440 mm/slub.c:4866
slab_free_after_rcu_debug+0x60/0x2a0 mm/slub.c:4717
rcu_do_batch kernel/rcu/tree.c:2605 [inline]
rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861
handle_softirqs+0x283/0x870 kernel/softirq.c:579
__do_softirq kernel/softirq.c:613 [inline]
invoke_softirq kernel/softirq.c:453 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1050
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa8/0x110 kernel/locking/spinlock.c:194
Code: 74 05 e8 4b 87 4b f6 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4f f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 93 2e 14 f6 65 8b 05 6c 71 24 07 85 c0 74 40 48 c7 04 24 0e 36
RSP: 0018:ffffc90003f6fc60 EFLAGS: 00000206
RAX: 237d7f7a06c71d00 RBX: 0000000000000a06 RCX: 237d7f7a06c71d00
RDX: 0000000000000006 RSI: ffffffff8d9b68b0 RDI: 0000000000000001
RBP: ffffc90003f6fcf0 R08: ffffffff8fa37e37 R09: 1ffffffff1f46fc6
R10: dffffc0000000000 R11: fffffbfff1f46fc7 R12: dffffc0000000000
R13: ffff8880641d6a40 R14: ffff888057cc1000 R15: 1ffff920007edf8c
__do_sys_perf_event_open kernel/events/core.c:13712 [inline]
__se_sys_perf_event_open+0x1942/0x1d70 kernel/events/core.c:13353
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd9da58ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd9db415038 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: ffffffffffffffda RBX: 00007fd9da7b5fa0 RCX: 00007fd9da58ebe9
RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 00002000000003c0
RBP: 00007fd9da611e19 R08: 0000000000000003 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd9da7b6038 R14: 00007fd9da7b5fa0 R15: 00007ffee6a22f78
</TASK>
Allocated by task 6980:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4365 [inline]
__kmalloc_node_noprof+0x276/0x4e0 mm/slub.c:4371
kmalloc_node_noprof include/linux/slab.h:932 [inline]
__bpf_map_area_alloc kernel/bpf/syscall.c:393 [inline]
bpf_map_area_alloc+0x64/0x180 kernel/bpf/syscall.c:406
prealloc_elems_and_freelist+0x86/0x1d0 kernel/bpf/stackmap.c:73
stack_map_alloc+0x33f/0x4c0 kernel/bpf/stackmap.c:136
map_create+0xaa3/0x14d0 kernel/bpf/syscall.c:1480
__sys_bpf+0x60f/0x870 kernel/bpf/syscall.c:6011
__do_sys_bpf kernel/bpf/syscall.c:6139 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6137 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6137
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
The buggy address belongs to the object at ffff88802fd43000
which belongs to the cache kmalloc-cg-1k of size 1024
The buggy address is located 24 bytes to the right of
allocated 576-byte region [ffff88802fd43000, ffff88802fd43240)
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2fd40
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff88806f32bf01
ksm flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a44b280 ffffea0001e83e00 dead000000000003
raw: 0000000000000000 0000000080100010 00000000f5000000 ffff88806f32bf01
head: 00fff00000000040 ffff88801a44b280 ffffea0001e83e00 dead000000000003
head: 0000000000000000 0000000080100010 00000000f5000000 ffff88806f32bf01
head: 00fff00000000003 ffffea0000bf5001 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5882, tgid 5882 (syz-executor), ts 81348212299, free_ts 80466086651
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2487 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2655
new_slab mm/slub.c:2709 [inline]
___slab_alloc+0xbeb/0x1410 mm/slub.c:3891
__slab_alloc mm/slub.c:3981 [inline]
__slab_alloc_node mm/slub.c:4056 [inline]
slab_alloc_node mm/slub.c:4217 [inline]
__do_kmalloc_node mm/slub.c:4364 [inline]
__kmalloc_noprof+0x305/0x4f0 mm/slub.c:4377
kmalloc_noprof include/linux/slab.h:909 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
__register_sysctl_table+0x72/0x1340 fs/proc/proc_sysctl.c:1379
neigh_sysctl_register+0x9a2/0xa80 net/core/neighbour.c:3887
devinet_sysctl_register+0xad/0x200 net/ipv4/devinet.c:2715
inetdev_init+0x2b4/0x500 net/ipv4/devinet.c:291
inetdev_event+0x301/0x15b0 net/ipv4/devinet.c:1591
notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
call_netdevice_notifiers net/core/dev.c:2281 [inline]
register_netdevice+0x1608/0x1ae0 net/core/dev.c:11227
__ip_tunnel_create+0x3e7/0x560 net/ipv4/ip_tunnel.c:268
ip_tunnel_init_net+0x2ba/0x800 net/ipv4/ip_tunnel.c:1161
page last free pid 5526 tgid 5526 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2895
discard_slab mm/slub.c:2753 [inline]
__put_partials+0x156/0x1a0 mm/slub.c:3218
put_cpu_partial+0x17c/0x250 mm/slub.c:3293
__slab_free+0x2d5/0x3c0 mm/slub.c:4550
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:340
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4180 [inline]
slab_alloc_node mm/slub.c:4229 [inline]
kmem_cache_alloc_node_noprof+0x1bb/0x3c0 mm/slub.c:4281
__alloc_skb+0x112/0x2d0 net/core/skbuff.c:659
alloc_skb include/linux/skbuff.h:1336 [inline]
alloc_skb_with_frags+0xca/0x890 net/core/skbuff.c:6665
sock_alloc_send_pskb+0x857/0x990 net/core/sock.c:2980
unix_dgram_sendmsg+0x461/0x1850 net/unix/af_unix.c:2153
sock_sendmsg_nosec net/socket.c:714 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:729
sock_write_iter+0x258/0x330 net/socket.c:1179
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c6/0xb30 fs/read_write.c:686
ksys_write+0x145/0x250 fs/read_write.c:738
Memory state around the buggy address:
ffff88802fd43100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88802fd43180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88802fd43200: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
^
ffff88802fd43280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802fd43300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
----------------
Code disassembly (best guess):
0: 74 05 je 0x7
2: e8 4b 87 4b f6 call 0xf64b8752
7: 48 c7 44 24 20 00 00 movq $0x0,0x20(%rsp)
e: 00 00
10: 9c pushf
11: 8f 44 24 20 pop 0x20(%rsp)
15: f6 44 24 21 02 testb $0x2,0x21(%rsp)
1a: 75 4f jne 0x6b
1c: f7 c3 00 02 00 00 test $0x200,%ebx
22: 74 01 je 0x25
24: fb sti
25: bf 01 00 00 00 mov $0x1,%edi
* 2a: e8 93 2e 14 f6 call 0xf6142ec2 <-- trapping instruction
2f: 65 8b 05 6c 71 24 07 mov %gs:0x724716c(%rip),%eax # 0x72471a2
36: 85 c0 test %eax,%eax
38: 74 40 je 0x7a
3a: 48 rex.W
3b: c7 .byte 0xc7
3c: 04 24 add $0x24,%al
3e: 0e (bad)
3f: 36 ss
Tested on:
commit: 71ca59e2 Merge branch 'fix-bpf_strnstr-len-error'
git tree: bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=127c3e62580000
kernel config: https://syzkaller.appspot.com/x/.config?x=807fffde4ddbe9ec
dashboard link: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch: https://syzkaller.appspot.com/x/patch.diff?x=1381fe62580000
© 2016 - 2025 Red Hat, Inc.