Re: [syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

Re: [syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-out-of-bounds Read in strnchr

==================================================================
BUG: KASAN: slab-out-of-bounds in strnchr+0x5e/0x80 lib/string.c:405
Read of size 1 at addr ffff8880796d9bb0 by task syz.0.17/6447

CPU: 1 UID: 0 PID: 6447 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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
 strnchr+0x5e/0x80 lib/string.c:405
 bpf_bprintf_prepare+0x167/0x13d0 kernel/bpf/helpers.c:829
 ____bpf_snprintf kernel/bpf/helpers.c:1065 [inline]
 bpf_snprintf+0xd3/0x1b0 kernel/bpf/helpers.c:1049
 bpf_prog_c2925c0a7ac12d80+0x58/0x60
 bpf_dispatcher_nop_func include/linux/bpf.h:1378 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run1+0x27f/0x4c0 kernel/trace/bpf_trace.c:2115
 __bpf_trace_rcu_utilization+0xa1/0xf0 include/trace/events/rcu.h:27
 __do_trace_rcu_utilization include/trace/events/rcu.h:27 [inline]
 trace_rcu_utilization+0x191/0x1c0 include/trace/events/rcu.h:27
 rcu_note_context_switch+0xc9/0x1120 kernel/rcu/tree_plugin.h:330
 __schedule+0x346/0x5000 kernel/sched/core.c:6748
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6960
 futex_do_wait kernel/futex/waitwake.c:358 [inline]
 __futex_wait+0x1c3/0x3d0 kernel/futex/waitwake.c:687
 futex_wait+0x104/0x360 kernel/futex/waitwake.c:715
 do_futex+0x333/0x420 kernel/futex/syscalls.c:130
 __do_sys_futex kernel/futex/syscalls.c:207 [inline]
 __se_sys_futex+0x36f/0x400 kernel/futex/syscalls.c:188
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe67538f749
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:00007fe6762900e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007fe6755e5fa8 RCX: 00007fe67538f749
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fe6755e5fa8
RBP: 00007fe6755e5fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe6755e6038 R14: 00007ffdb1d360a0 R15: 00007ffdb1d36188
 </TASK>

Allocated by task 6447:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
 poison_kmalloc_redzone mm/kasan/common.c:397 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:414
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5657 [inline]
 __kmalloc_node_noprof+0x57a/0x820 mm/slub.c:5663
 kmalloc_node_noprof include/linux/slab.h:987 [inline]
 __bpf_map_area_alloc kernel/bpf/syscall.c:395 [inline]
 bpf_map_area_alloc+0x64/0x180 kernel/bpf/syscall.c:408
 insn_array_alloc+0x52/0x140 kernel/bpf/bpf_insn_array.c:49
 map_create+0xafd/0x16a0 kernel/bpf/syscall.c:1514
 __sys_bpf+0x5f0/0x860 kernel/bpf/syscall.c:6146
 __do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6272
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880796d9800
 which belongs to the cache kmalloc-cg-1k of size 1024
The buggy address is located 0 bytes to the right of
 allocated 944-byte region [ffff8880796d9800, ffff8880796d9bb0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x796d8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff8880783cfa01
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813ffb0280 dead000000000122 0000000000000000
raw: 0000000000000000 0000000080100010 00000000f5000000 ffff8880783cfa01
head: 00fff00000000040 ffff88813ffb0280 dead000000000122 0000000000000000
head: 0000000000000000 0000000080100010 00000000f5000000 ffff8880783cfa01
head: 00fff00000000003 ffffea0001e5b601 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 6341, tgid 6341 (syz-executor), ts 133223797627, free_ts 133152404370
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1846
 prep_new_page mm/page_alloc.c:1854 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3915
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2486
 alloc_slab_page mm/slub.c:3075 [inline]
 allocate_slab+0x86/0x3b0 mm/slub.c:3248
 new_slab mm/slub.c:3302 [inline]
 ___slab_alloc+0xf2b/0x1960 mm/slub.c:4656
 __slab_alloc+0x65/0x100 mm/slub.c:4779
 __slab_alloc_node mm/slub.c:4855 [inline]
 slab_alloc_node mm/slub.c:5251 [inline]
 __do_kmalloc_node mm/slub.c:5656 [inline]
 __kvmalloc_node_noprof+0x6b6/0x920 mm/slub.c:7134
 xt_alloc_table_info+0x40/0xb0 net/netfilter/x_tables.c:1193
 do_replace net/ipv6/netfilter/ip6_tables.c:1143 [inline]
 do_ip6t_set_ctl+0x88a/0xce0 net/ipv6/netfilter/ip6_tables.c:1644
 nf_setsockopt+0x26f/0x290 net/netfilter/nf_sockopt.c:101
 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2322
 __sys_setsockopt net/socket.c:2347 [inline]
 __do_sys_setsockopt net/socket.c:2353 [inline]
 __se_sys_setsockopt net/socket.c:2350 [inline]
 __x64_sys_setsockopt+0x13f/0x1b0 net/socket.c:2350
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 6341 tgid 6341 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0xbc8/0xd30 mm/page_alloc.c:2943
 discard_slab mm/slub.c:3346 [inline]
 __put_partials+0x146/0x170 mm/slub.c:3886
 put_cpu_partial+0x1f2/0x2d0 mm/slub.c:3961
 __slab_free+0x288/0x2a0 mm/slub.c:5952
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:349
 kasan_slab_alloc include/linux/kasan.h:252 [inline]
 slab_post_alloc_hook mm/slub.c:4953 [inline]
 slab_alloc_node mm/slub.c:5263 [inline]
 __do_kmalloc_node mm/slub.c:5656 [inline]
 __kmalloc_node_track_caller_noprof+0x526/0x820 mm/slub.c:5764
 __kmemdup_nul mm/util.c:64 [inline]
 kstrdup+0x42/0x100 mm/util.c:84
 __kernfs_new_node+0x9c/0x880 fs/kernfs/dir.c:633
 kernfs_new_node+0x102/0x210 fs/kernfs/dir.c:716
 kernfs_create_link+0xa7/0x200 fs/kernfs/symlink.c:39
 sysfs_do_create_link_sd+0x83/0x110 fs/sysfs/symlink.c:44
 driver_sysfs_add+0x89/0x210 drivers/base/dd.c:442
 device_bind_driver+0x17/0x60 drivers/base/dd.c:500
 mac80211_hwsim_new_radio+0x4a0/0x5320 drivers/net/wireless/virtual/mac80211_hwsim.c:5436

Memory state around the buggy address:
 ffff8880796d9a80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880796d9b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880796d9b80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
                                     ^
 ffff8880796d9c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880796d9c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


Tested on:

commit:         22cc16c0 riscv, bpf: Fix incorrect usage of BPF_TRAMP_..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=15cb692a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=2c29addf92581b410079
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=12950e9a580000

Re: [syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com
Tested-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com

Tested on:

commit:         ab86d0bf selftests/bpf: Update xdp_context_test_run te..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=13c6c1fc580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=2c29addf92581b410079
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=16ccef92580000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

[Edward Adam Davis]

#syz test

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index db72b96f9c8c..88da2d0e634c 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -827,7 +827,7 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
 	char fmt_ptype, cur_ip[16], ip_spec[] = "%pXX";
 
 	fmt_end = strnchr(fmt, fmt_size, 0);
-	if (!fmt_end)
+	if (!fmt_end || fmt_end == fmt)
 		return -EINVAL;
 	fmt_size = fmt_end - fmt;
 

Re: [syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com
Tested-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com

Tested on:

commit:         22cc16c0 riscv, bpf: Fix incorrect usage of BPF_TRAMP_..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=15ef2074580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=2c29addf92581b410079
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=13a15e9a580000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-out-of-bounds Read in strnchr

==================================================================
BUG: KASAN: slab-out-of-bounds in strnchr+0x5e/0x80 lib/string.c:405
Read of size 1 at addr ffff888029166bb0 by task syz.0.17/6458

CPU: 0 UID: 0 PID: 6458 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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
 strnchr+0x5e/0x80 lib/string.c:405
 bpf_bprintf_prepare+0x167/0x13d0 kernel/bpf/helpers.c:829
 ____bpf_snprintf kernel/bpf/helpers.c:1065 [inline]
 bpf_snprintf+0xd3/0x1b0 kernel/bpf/helpers.c:1049
 bpf_prog_c2925c0a7ac12d80+0x58/0x60
 bpf_dispatcher_nop_func include/linux/bpf.h:1378 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run1+0x27f/0x4c0 kernel/trace/bpf_trace.c:2115
 __bpf_trace_rcu_utilization+0xa1/0xf0 include/trace/events/rcu.h:27
 __do_trace_rcu_utilization include/trace/events/rcu.h:27 [inline]
 trace_rcu_utilization+0x191/0x1c0 include/trace/events/rcu.h:27
 rcu_note_context_switch+0xc9/0x1120 kernel/rcu/tree_plugin.h:330
 __schedule+0x346/0x5000 kernel/sched/core.c:6748
 preempt_schedule_common+0x83/0xd0 kernel/sched/core.c:7047
 preempt_schedule+0xae/0xc0 kernel/sched/core.c:7071
 preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12
 class_preempt_destructor include/linux/preempt.h:468 [inline]
 try_to_wake_up+0x82b/0x12b0 kernel/sched/core.c:4225
 wake_up_process kernel/sched/core.c:4349 [inline]
 wake_up_q+0x85/0xd0 kernel/sched/core.c:1087
 futex_wake+0x4a0/0x560 kernel/futex/waitwake.c:198
 do_futex+0x395/0x420 kernel/futex/syscalls.c:135
 __do_sys_futex kernel/futex/syscalls.c:207 [inline]
 __se_sys_futex+0x36f/0x400 kernel/futex/syscalls.c:188
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f540bd8f749
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:00007f540cc950e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007f540bfe5fa8 RCX: 00007f540bd8f749
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f540bfe5fac
RBP: 00007f540bfe5fa0 R08: 3fffffffffffffff R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f540bfe6038 R14: 00007ffe4f3ebe10 R15: 00007ffe4f3ebef8
 </TASK>

Allocated by task 6458:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
 poison_kmalloc_redzone mm/kasan/common.c:397 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:414
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5657 [inline]
 __kmalloc_node_noprof+0x57a/0x820 mm/slub.c:5663
 kmalloc_node_noprof include/linux/slab.h:987 [inline]
 __bpf_map_area_alloc kernel/bpf/syscall.c:395 [inline]
 bpf_map_area_alloc+0x64/0x180 kernel/bpf/syscall.c:408
 insn_array_alloc+0x52/0x140 kernel/bpf/bpf_insn_array.c:49
 map_create+0xafd/0x16a0 kernel/bpf/syscall.c:1514
 __sys_bpf+0x5f0/0x860 kernel/bpf/syscall.c:6146
 __do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6272
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888029166800
 which belongs to the cache kmalloc-cg-1k of size 1024
The buggy address is located 0 bytes to the right of
 allocated 944-byte region [ffff888029166800, ffff888029166bb0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x29160
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff8880287ecb01
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813ffb0280 ffffea0000c50e00 dead000000000002
raw: 0000000000000000 0000000080100010 00000000f5000000 ffff8880287ecb01
head: 00fff00000000040 ffff88813ffb0280 ffffea0000c50e00 dead000000000002
head: 0000000000000000 0000000080100010 00000000f5000000 ffff8880287ecb01
head: 00fff00000000003 ffffea0000a45801 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 5651, tgid 5651 (dhcpcd-run-hook), ts 58371581863, free_ts 57441834104
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1846
 prep_new_page mm/page_alloc.c:1854 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3915
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2486
 alloc_slab_page mm/slub.c:3075 [inline]
 allocate_slab+0x86/0x3b0 mm/slub.c:3248
 new_slab mm/slub.c:3302 [inline]
 ___slab_alloc+0xf2b/0x1960 mm/slub.c:4656
 __slab_alloc+0x65/0x100 mm/slub.c:4779
 __slab_alloc_node mm/slub.c:4855 [inline]
 slab_alloc_node mm/slub.c:5251 [inline]
 __do_kmalloc_node mm/slub.c:5656 [inline]
 __kmalloc_noprof+0x47d/0x800 mm/slub.c:5669
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kmalloc_array_noprof include/linux/slab.h:1003 [inline]
 alloc_pipe_info+0x1fd/0x4d0 fs/pipe.c:817
 get_pipe_inode fs/pipe.c:896 [inline]
 create_pipe_files+0x8a/0x7e0 fs/pipe.c:928
 __do_pipe_flags+0x46/0x1f0 fs/pipe.c:990
 do_pipe2+0x9c/0x170 fs/pipe.c:1038
 __do_sys_pipe2 fs/pipe.c:1056 [inline]
 __se_sys_pipe2 fs/pipe.c:1054 [inline]
 __x64_sys_pipe2+0x5a/0x70 fs/pipe.c:1054
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5493 tgid 5493 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0xbc8/0xd30 mm/page_alloc.c:2943
 discard_slab mm/slub.c:3346 [inline]
 __put_partials+0x146/0x170 mm/slub.c:3886
 put_cpu_partial+0x1f2/0x2d0 mm/slub.c:3961
 __slab_free+0x288/0x2a0 mm/slub.c:5952
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:349
 kasan_slab_alloc include/linux/kasan.h:252 [inline]
 slab_post_alloc_hook mm/slub.c:4953 [inline]
 slab_alloc_node mm/slub.c:5263 [inline]
 kmem_cache_alloc_node_noprof+0x43c/0x720 mm/slub.c:5315
 __alloc_skb+0x255/0x430 net/core/skbuff.c:679
 alloc_skb include/linux/skbuff.h:1383 [inline]
 alloc_skb_with_frags+0xca/0x890 net/core/skbuff.c:6712
 sock_alloc_send_pskb+0x84d/0x980 net/core/sock.c:2995
 unix_dgram_sendmsg+0x454/0x1840 net/unix/af_unix.c:2130
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 sock_write_iter+0x279/0x360 net/socket.c:1195
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5c9/0xb30 fs/read_write.c:686
 ksys_write+0x145/0x250 fs/read_write.c:738

Memory state around the buggy address:
 ffff888029166a80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888029166b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888029166b80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
                                     ^
 ffff888029166c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888029166c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


Tested on:

commit:         22cc16c0 riscv, bpf: Fix incorrect usage of BPF_TRAMP_..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=156d7efc580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=2c29addf92581b410079
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=11f90e9a580000

[syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    22cc16c04b78 riscv, bpf: Fix incorrect usage of BPF_TRAMP_..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=1391f792580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=2c29addf92581b410079
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=10c82e22580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16de569a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/43a53493cb5f/disk-22cc16c0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9726fb9e1980/vmlinux-22cc16c0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/efd2bc050ab6/bzImage-22cc16c0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in strnchr+0x5e/0x80 lib/string.c:405
Read of size 1 at addr ffff888029e093b0 by task ksoftirqd/1/23

CPU: 1 UID: 0 PID: 23 Comm: ksoftirqd/1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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
 strnchr+0x5e/0x80 lib/string.c:405
 bpf_bprintf_prepare+0x167/0x13d0 kernel/bpf/helpers.c:829
 ____bpf_snprintf kernel/bpf/helpers.c:1065 [inline]
 bpf_snprintf+0xd3/0x1b0 kernel/bpf/helpers.c:1049
 bpf_prog_c2925c0a7ac12d80+0x58/0x60
 bpf_dispatcher_nop_func include/linux/bpf.h:1378 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run1+0x27f/0x4c0 kernel/trace/bpf_trace.c:2115
 __bpf_trace_rcu_utilization+0xa1/0xf0 include/trace/events/rcu.h:27
 __do_trace_rcu_utilization include/trace/events/rcu.h:27 [inline]
 trace_rcu_utilization+0x191/0x1c0 include/trace/events/rcu.h:27
 rcu_core+0x13fe/0x1870 kernel/rcu/tree.c:2865
 handle_softirqs+0x27d/0x850 kernel/softirq.c:622
 run_ksoftirqd+0x9b/0x100 kernel/softirq.c:1063
 smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>

Allocated by task 6022:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
 poison_kmalloc_redzone mm/kasan/common.c:397 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:414
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5657 [inline]
 __kmalloc_node_noprof+0x57a/0x820 mm/slub.c:5663
 kmalloc_node_noprof include/linux/slab.h:987 [inline]
 __bpf_map_area_alloc kernel/bpf/syscall.c:395 [inline]
 bpf_map_area_alloc+0x64/0x180 kernel/bpf/syscall.c:408
 insn_array_alloc+0x52/0x140 kernel/bpf/bpf_insn_array.c:49
 map_create+0xafd/0x16a0 kernel/bpf/syscall.c:1514
 __sys_bpf+0x5f0/0x860 kernel/bpf/syscall.c:6146
 __do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6272
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888029e09000
 which belongs to the cache kmalloc-cg-1k of size 1024
The buggy address is located 0 bytes to the right of
 allocated 944-byte region [ffff888029e09000, ffff888029e093b0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x29e08
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff888072141701
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813ffb0280 dead000000000100 dead000000000122
raw: 0000000000000000 0000000080100010 00000000f5000000 ffff888072141701
head: 00fff00000000040 ffff88813ffb0280 dead000000000100 dead000000000122
head: 0000000000000000 0000000080100010 00000000f5000000 ffff888072141701
head: 00fff00000000003 ffffea0000a78201 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 5709, tgid 5709 (dhcpcd-run-hook), ts 83835394493, free_ts 83796353079
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1846
 prep_new_page mm/page_alloc.c:1854 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3915
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2486
 alloc_slab_page mm/slub.c:3075 [inline]
 allocate_slab+0x86/0x3b0 mm/slub.c:3248
 new_slab mm/slub.c:3302 [inline]
 ___slab_alloc+0xf2b/0x1960 mm/slub.c:4656
 __slab_alloc+0x65/0x100 mm/slub.c:4779
 __slab_alloc_node mm/slub.c:4855 [inline]
 slab_alloc_node mm/slub.c:5251 [inline]
 __do_kmalloc_node mm/slub.c:5656 [inline]
 __kmalloc_noprof+0x47d/0x800 mm/slub.c:5669
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kmalloc_array_noprof include/linux/slab.h:1003 [inline]
 alloc_pipe_info+0x1fd/0x4d0 fs/pipe.c:817
 get_pipe_inode fs/pipe.c:896 [inline]
 create_pipe_files+0x8a/0x7e0 fs/pipe.c:928
 __do_pipe_flags+0x46/0x1f0 fs/pipe.c:990
 do_pipe2+0x9c/0x170 fs/pipe.c:1038
 __do_sys_pipe2 fs/pipe.c:1056 [inline]
 __se_sys_pipe2 fs/pipe.c:1054 [inline]
 __x64_sys_pipe2+0x5a/0x70 fs/pipe.c:1054
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5712 tgid 5712 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0xbc8/0xd30 mm/page_alloc.c:2943
 __slab_free+0x21b/0x2a0 mm/slub.c:6004
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:349
 kasan_slab_alloc include/linux/kasan.h:252 [inline]
 slab_post_alloc_hook mm/slub.c:4953 [inline]
 slab_alloc_node mm/slub.c:5263 [inline]
 kmem_cache_alloc_noprof+0x37d/0x710 mm/slub.c:5270
 vm_area_alloc+0x24/0x140 mm/vma_init.c:32
 __mmap_new_vma mm/vma.c:2469 [inline]
 __mmap_region mm/vma.c:2708 [inline]
 mmap_region+0xdea/0x1d10 mm/vma.c:2786
 do_mmap+0xc45/0x10d0 mm/mmap.c:558
 vm_mmap_pgoff+0x2a6/0x4d0 mm/util.c:581
 ksys_mmap_pgoff+0x51f/0x760 mm/mmap.c:604
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888029e09280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888029e09300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888029e09380: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
                                     ^
 ffff888029e09400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888029e09480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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