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KASAN: slab-use-after-free Read in seq_printf

Status: moderation: reported on 2025/10/07 11:49
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+3366add91c4b8d9822cf@syzkaller.appspotmail.com
First crash: 100d, last: 3d22h
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-out-of-bounds Read in seq_printf fs 19 5 245d 350d 0/29 auto-obsoleted due to no activity on 2025/08/09 17:54
upstream KMSAN: uninit-value in seq_printf (2) fs 7 C 99 1306d 1573d 0/29 auto-closed as invalid on 2022/09/30 02:43
android-5-10 KASAN: use-after-free Read in seq_printf 19 15 109d 217d 0/2 auto-obsoleted due to no activity on 2025/12/23 06:43
upstream KMSAN: kernel-infoleak in __skb_datagram_iter net 9 68 838d 943d 23/29 fixed on 2023/09/28 17:51
android-6-1 KASAN: slab-out-of-bounds Read in seq_printf 19 2 114d 118d 0/2 auto-obsoleted due to no activity on 2025/12/19 00:57
android-5-15 KASAN: use-after-free Read in seq_printf 19 1 115d 115d 0/2 auto-obsoleted due to no activity on 2025/12/17 23:30

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in string_nocheck lib/vsprintf.c:654 [inline]
BUG: KASAN: slab-use-after-free in string+0x231/0x2b0 lib/vsprintf.c:736
Read of size 1 at addr ffff888059a15a20 by task syz.1.395/7511

CPU: 1 UID: 0 PID: 7511 Comm: syz.1.395 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 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
 string_nocheck lib/vsprintf.c:654 [inline]
 string+0x231/0x2b0 lib/vsprintf.c:736
 vsnprintf+0x739/0xee0 lib/vsprintf.c:2947
 seq_vprintf fs/seq_file.c:391 [inline]
 seq_printf+0x178/0x270 fs/seq_file.c:406
 input_devices_seq_show+0x145/0x640 drivers/input/input.c:1099
 seq_read_iter+0x9bb/0xe20 fs/seq_file.c:272
 seq_read+0x369/0x480 fs/seq_file.c:162
 pde_read fs/proc/inode.c:308 [inline]
 proc_reg_read+0x1e9/0x2e0 fs/proc/inode.c:320
 do_loop_readv_writev fs/read_write.c:847 [inline]
 vfs_readv+0x5aa/0x850 fs/read_write.c:1020
 do_preadv fs/read_write.c:1132 [inline]
 __do_sys_preadv fs/read_write.c:1179 [inline]
 __se_sys_preadv fs/read_write.c:1174 [inline]
 __x64_sys_preadv+0x197/0x2a0 fs/read_write.c:1174
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3fbc58f749
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:00007f3fbd4ec038 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 00007f3fbc7e5fa0 RCX: 00007f3fbc58f749
RDX: 0000000000000001 RSI: 00002000000015c0 RDI: 0000000000000003
RBP: 00007f3fbc613f91 R08: 0000000000207fff R09: 0000000000000000
R10: 00000000000000f2 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3fbc7e6038 R14: 00007f3fbc7e5fa0 R15: 00007f3fbc90fa28
 </TASK>

Allocated by task 7472:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5657 [inline]
 __kmalloc_noprof+0x41d/0x800 mm/slub.c:5669
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 ieee802_11_parse_elems_full+0x152/0x2ab0 net/mac80211/parse.c:1031
 ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2469 [inline]
 ieee80211_inform_bss+0x147/0x1130 net/mac80211/scan.c:79
 rdev_inform_bss net/wireless/rdev-ops.h:418 [inline]
 cfg80211_inform_single_bss_data+0xd14/0x1ad0 net/wireless/scan.c:2373
 cfg80211_inform_bss_data+0x203/0x3b40 net/wireless/scan.c:3228
 cfg80211_inform_bss_frame_data+0x3c7/0x710 net/wireless/scan.c:3319
 ieee80211_bss_info_update+0x749/0x9e0 net/mac80211/scan.c:230
 ieee80211_scan_rx+0x593/0xa20 net/mac80211/scan.c:359
 __ieee80211_rx_handle_packet net/mac80211/rx.c:5287 [inline]
 ieee80211_rx_list+0x2485/0x2f90 net/mac80211/rx.c:5544
 ieee80211_rx_napi+0x1a8/0x3d0 net/mac80211/rx.c:5567
 ieee80211_rx include/net/mac80211.h:5216 [inline]
 ieee80211_handle_queued_frames+0xe8/0x1e0 net/mac80211/main.c:452
 tasklet_action_common+0x2da/0x4b0 kernel/softirq.c:925
 handle_softirqs+0x22b/0x7c0 kernel/softirq.c:622
 do_softirq+0x76/0xd0 kernel/softirq.c:523
 __local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 ip_mc_clear_src net/ipv4/igmp.c:2253 [inline]
 __ip_mc_dec_group+0x4c7/0x670 net/ipv4/igmp.c:1780
 inetdev_event+0x297/0x15b0 net/ipv4/devinet.c:1641
 notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
 call_netdevice_notifiers net/core/dev.c:2282 [inline]
 __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
 netif_change_flags+0xe8/0x1a0 net/core/dev.c:9804
 do_setlink+0xc55/0x41c0 net/core/rtnetlink.c:3158
 rtnl_group_changelink net/core/rtnetlink.c:3790 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3944 [inline]
 rtnl_newlink+0x14b0/0x1c90 net/core/rtnetlink.c:4072
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 ____sys_sendmsg+0x505/0x820 net/socket.c:2592
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2646
 __sys_sendmsg net/socket.c:2678 [inline]
 __do_sys_sendmsg net/socket.c:2683 [inline]
 __se_sys_sendmsg net/socket.c:2681 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2681
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 7472:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2540 [inline]
 slab_free mm/slub.c:6670 [inline]
 kfree+0x1c0/0x660 mm/slub.c:6878
 ieee80211_inform_bss+0xc4e/0x1130 net/mac80211/scan.c:164
 rdev_inform_bss net/wireless/rdev-ops.h:418 [inline]
 cfg80211_inform_single_bss_data+0xd14/0x1ad0 net/wireless/scan.c:2373
 cfg80211_inform_bss_data+0x203/0x3b40 net/wireless/scan.c:3228
 cfg80211_inform_bss_frame_data+0x3c7/0x710 net/wireless/scan.c:3319
 ieee80211_bss_info_update+0x749/0x9e0 net/mac80211/scan.c:230
 ieee80211_scan_rx+0x593/0xa20 net/mac80211/scan.c:359
 __ieee80211_rx_handle_packet net/mac80211/rx.c:5287 [inline]
 ieee80211_rx_list+0x2485/0x2f90 net/mac80211/rx.c:5544
 ieee80211_rx_napi+0x1a8/0x3d0 net/mac80211/rx.c:5567
 ieee80211_rx include/net/mac80211.h:5216 [inline]
 ieee80211_handle_queued_frames+0xe8/0x1e0 net/mac80211/main.c:452
 tasklet_action_common+0x2da/0x4b0 kernel/softirq.c:925
 handle_softirqs+0x22b/0x7c0 kernel/softirq.c:622
 do_softirq+0x76/0xd0 kernel/softirq.c:523
 __local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 ip_mc_clear_src net/ipv4/igmp.c:2253 [inline]
 __ip_mc_dec_group+0x4c7/0x670 net/ipv4/igmp.c:1780
 inetdev_event+0x297/0x15b0 net/ipv4/devinet.c:1641
 notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
 call_netdevice_notifiers net/core/dev.c:2282 [inline]
 __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
 netif_change_flags+0xe8/0x1a0 net/core/dev.c:9804
 do_setlink+0xc55/0x41c0 net/core/rtnetlink.c:3158
 rtnl_group_changelink net/core/rtnetlink.c:3790 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3944 [inline]
 rtnl_newlink+0x14b0/0x1c90 net/core/rtnetlink.c:4072
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 ____sys_sendmsg+0x505/0x820 net/socket.c:2592
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2646
 __sys_sendmsg net/socket.c:2678 [inline]
 __do_sys_sendmsg net/socket.c:2683 [inline]
 __se_sys_sendmsg net/socket.c:2681 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2681
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888059a15800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 544 bytes inside of
 freed 1024-byte region [ffff888059a15800, ffff888059a15c00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x59a10
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813ffa6dc0 ffffea0001333000 dead000000000002
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813ffa6dc0 ffffea0001333000 dead000000000002
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0001668401 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 0x52820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 36, tgid 36 (kworker/u8:2), ts 110548083117, free_ts 39099257608
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1857
 prep_new_page mm/page_alloc.c:1865 [inline]
 get_page_from_freelist+0x24e0/0x2580 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+0xe53/0x1820 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]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 ieee802_11_parse_elems_full+0x152/0x2ab0 net/mac80211/parse.c:1031
 ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2469 [inline]
 ieee80211_inform_bss+0x147/0x1130 net/mac80211/scan.c:79
 rdev_inform_bss net/wireless/rdev-ops.h:418 [inline]
 cfg80211_inform_single_bss_data+0xd14/0x1ad0 net/wireless/scan.c:2373
 cfg80211_inform_bss_data+0x203/0x3b40 net/wireless/scan.c:3228
 cfg80211_inform_bss_frame_data+0x3c7/0x710 net/wireless/scan.c:3319
 ieee80211_bss_info_update+0x749/0x9e0 net/mac80211/scan.c:230
 ieee80211_scan_rx+0x593/0xa20 net/mac80211/scan.c:359
 __ieee80211_rx_handle_packet net/mac80211/rx.c:5287 [inline]
 ieee80211_rx_list+0x2485/0x2f90 net/mac80211/rx.c:5544
page last free pid 1 tgid 1 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1406 [inline]
 __free_frozen_pages+0xbc8/0xd30 mm/page_alloc.c:2943
 __free_pages mm/page_alloc.c:5329 [inline]
 free_contig_range+0x1bd/0x490 mm/page_alloc.c:7197
 destroy_args+0x69/0x660 mm/debug_vm_pgtable.c:983
 debug_vm_pgtable+0x38f/0x3a0 mm/debug_vm_pgtable.c:1372
 do_one_initcall+0x1f1/0x800 init/main.c:1378
 do_initcall_level+0x104/0x190 init/main.c:1440
 do_initcalls+0x59/0xa0 init/main.c:1456
 kernel_init_freeable+0x2a7/0x3d0 init/main.c:1688
 kernel_init+0x1d/0x1d0 init/main.c:1578
 ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

Memory state around the buggy address:
 ffff888059a15900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888059a15980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888059a15a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff888059a15a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888059a15b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/08 06:25 upstream f0b9d8eb98df d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce KASAN: slab-use-after-free Read in seq_printf
2025/12/18 22:23 upstream ea1013c15392 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: slab-use-after-free Read in seq_printf
2025/10/26 18:17 upstream 72761a7e3122 c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce KASAN: slab-use-after-free Read in seq_printf
2025/10/03 11:42 upstream e406d57be7bd 49379ee0 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce KASAN: slab-use-after-free Read in seq_printf
2026/01/01 10:13 upstream 9528d5c091c5 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 KASAN: slab-use-after-free Read in seq_printf
* Struck through repros no longer work on HEAD.