[syzbot] [bpf?] KASAN: stack-out-of-bounds Write in __bpf_get_stack

syzbot
2025-11-10T18:41:33Z

Hello,

syzbot found the following issue on:

HEAD commit: f8c67d8550ee bpf: Use kmalloc_nolock() in range tree
git tree: bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=121a50b4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e46b8a1c645465a9
dashboard link: https://syzkaller.appspot.com/bug?extid=d1b7fa1092def3628bd7
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12270412580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=128bd084580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d9e95bfbe4ee/disk-f8c67d85.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0766b6dd0e91/vmlinux-f8c67d85.xz
kernel image: https://storage.googleapis.com/syzbot-assets/79089f9e9e93/bzImage-f8c67d85.xz

The issue was bisected to:

commit e17d62fedd10ae56e2426858bd0757da544dbc73
Author: Arnaud Lecomte <contact@arnaud-lcm.com>
Date: Sat Oct 25 19:28:58 2025 +0000

bpf: Refactor stack map trace depth calculation into helper function

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1632d0b4580000
final oops: https://syzkaller.appspot.com/x/report.txt?x=1532d0b4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1132d0b4580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d1b7fa1092def3628bd7@syzkaller.appspotmail.com
Fixes: e17d62fedd10 ("bpf: Refactor stack map trace depth calculation into helper function")

==================================================================
BUG: KASAN: stack-out-of-bounds in __bpf_get_stack+0x5a3/0xaa0 kernel/bpf/stackmap.c:493
Write of size 168 at addr ffffc900030e73a8 by task syz.1.44/6108

CPU: 0 UID: 0 PID: 6108 Comm: syz.1.44 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
<TASK>
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
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:200
__asan_memcpy+0x40/0x70 mm/kasan/shadow.c:106
__bpf_get_stack+0x5a3/0xaa0 kernel/bpf/stackmap.c:493
____bpf_get_stack kernel/bpf/stackmap.c:517 [inline]
bpf_get_stack+0x33/0x50 kernel/bpf/stackmap.c:514
____bpf_get_stack_raw_tp kernel/trace/bpf_trace.c:1653 [inline]
bpf_get_stack_raw_tp+0x1a9/0x220 kernel/trace/bpf_trace.c:1643
bpf_prog_4b3f8e3d902f6f0d+0x41/0x49
bpf_dispatcher_nop_func include/linux/bpf.h:1364 [inline]
__bpf_prog_run include/linux/filter.h:721 [inline]
bpf_prog_run include/linux/filter.h:728 [inline]
__bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
bpf_trace_run2+0x284/0x4b0 kernel/trace/bpf_trace.c:2116
__traceiter_kfree+0x2e/0x50 include/trace/events/kmem.h:97
__do_trace_kfree include/trace/events/kmem.h:97 [inline]
trace_kfree include/trace/events/kmem.h:97 [inline]
kfree+0x62f/0x6d0 mm/slub.c:6824
compute_scc+0x9a6/0xa20 kernel/bpf/verifier.c:25021
bpf_check+0x5df2/0x1c210 kernel/bpf/verifier.c:25162
bpf_prog_load+0x13ba/0x1a10 kernel/bpf/syscall.c:3095
__sys_bpf+0x507/0x860 kernel/bpf/syscall.c:6171
__do_sys_bpf kernel/bpf/syscall.c:6281 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6279 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6279
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc4d8b8f6c9
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:00007ffcd2851bb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007fc4d8de5fa0 RCX: 00007fc4d8b8f6c9
RDX: 0000000000000094 RSI: 00002000000000c0 RDI: 0000000000000005
RBP: 00007fc4d8c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc4d8de5fa0 R14: 00007fc4d8de5fa0 R15: 0000000000000003
</TASK>

The buggy address belongs to stack of task syz.1.44/6108
and is located at offset 296 in frame:
__bpf_get_stack+0x0/0xaa0 include/linux/mmap_lock.h:-1

This frame has 1 object:
[32, 36) 'rctx.i'

The buggy address belongs to a 8-page vmalloc region starting at 0xffffc900030e0000 allocated at copy_process+0x54b/0x3c00 kernel/fork.c:2012
The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x572fb
memcg:ffff88803037aa02
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 0000000000000000 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff ffff88803037aa02
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x2dc2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_ZERO|__GFP_NOWARN), pid 1340, tgid 1340 (kworker/u8:6), ts 107851542040, free_ts 101175357499
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1850
prep_new_page mm/page_alloc.c:1858 [inline]
get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3884
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5183
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_frozen_pages_noprof mm/mempolicy.c:2487 [inline]
alloc_pages_noprof+0xa9/0x190 mm/mempolicy.c:2507
vm_area_alloc_pages mm/vmalloc.c:3647 [inline]
__vmalloc_area_node mm/vmalloc.c:3724 [inline]
__vmalloc_node_range_noprof+0x96c/0x12d0 mm/vmalloc.c:3897
__vmalloc_node_noprof+0xc2/0x110 mm/vmalloc.c:3960
alloc_thread_stack_node kernel/fork.c:311 [inline]
dup_task_struct+0x3d4/0x830 kernel/fork.c:881
copy_process+0x54b/0x3c00 kernel/fork.c:2012
kernel_clone+0x21e/0x840 kernel/fork.c:2609
user_mode_thread+0xdd/0x140 kernel/fork.c:2685
call_usermodehelper_exec_sync kernel/umh.c:132 [inline]
call_usermodehelper_exec_work+0x9c/0x230 kernel/umh.c:163
process_one_work kernel/workqueue.c:3263 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
page last free pid 5918 tgid 5918 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1394 [inline]
__free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2906
vfree+0x25a/0x400 mm/vmalloc.c:3440
kcov_put kernel/kcov.c:439 [inline]
kcov_close+0x28/0x50 kernel/kcov.c:535
__fput+0x44c/0xa70 fs/file_table.c:468
task_work_run+0x1d4/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x6b5/0x2300 kernel/exit.c:966
do_group_exit+0x21c/0x2d0 kernel/exit.c:1107
get_signal+0x1285/0x1340 kernel/signal.c:3034
arch_do_signal_or_restart+0xa0/0x790 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x72/0x130 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x2bd/0xfa0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffffc900030e7300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc900030e7380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc900030e7400: f1 f1 f1 f1 00 00 f2 f2 00 00 f3 f3 00 00 00 00
^
ffffc900030e7480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc900030e7500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

---
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