KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname

Status: upstream: reported C repro on 2026/08/07 16:20
Reported-by: syzbot+aa3992db0ca16a888f46@syzkaller.appspotmail.com
First crash: 53d, last: 15d
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname origin:lts-only 19 syz, C 57 4h27m 56d 0/3 upstream: reported C repro on 2026/08/04 16:29
▶ ▼ Last patch testing requests (3)
Created Duration User Patch Repo Result
2026/09/30 01:27 0m retest repro linux-5.15.y error job log
2026/09/30 01:27 0m retest repro linux-5.15.y error job log
2026/09/30 01:27 0m retest repro linux-5.15.y error job log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in string_nocheck lib/vsprintf.c:642 [inline]
BUG: KASAN: use-after-free in string+0x204/0x290 lib/vsprintf.c:724
Read of size 1 at addr ffff888071136260 by task cifsd/4400

CPU: 0 PID: 4400 Comm: cifsd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 string_nocheck lib/vsprintf.c:642 [inline]
 string+0x204/0x290 lib/vsprintf.c:724
 vsnprintf+0x10db/0x1c20 lib/vsprintf.c:2811
 vscnprintf lib/vsprintf.c:2914 [inline]
 scnprintf+0xe5/0x180 lib/vsprintf.c:2968
 reconn_set_ipaddr_from_hostname+0x112/0x580 fs/cifs/connect.c:107
 __cifs_reconnect fs/cifs/connect.c:288 [inline]
 cifs_reconnect+0x470/0x1350 fs/cifs/connect.c:447
 cifs_demultiplex_thread+0x1eca/0x35b0 fs/cifs/connect.c:-1
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Allocated by task 4399:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xaf/0xe0 mm/kasan/common.c:522
 kstrdup+0x32/0x70 mm/util.c:60
 cifs_get_tcp_session+0xde/0x18f0 fs/cifs/connect.c:1431
 mount_get_conns+0xc3/0xe00 fs/cifs/connect.c:2988
 is_dfs_mount fs/cifs/connect.c:3354 [inline]
 cifs_mount+0x162/0x1380 fs/cifs/connect.c:3549
 cifs_smb3_do_mount+0x366/0x760 fs/cifs/cifsfs.c:895
 smb3_get_tree_common fs/cifs/fs_context.c:708 [inline]
 smb3_get_tree+0x59a/0xa80 fs/cifs/fs_context.c:726
 vfs_get_tree+0x88/0x270 fs/super.c:1530
 do_new_mount+0x247/0xa40 fs/namespace.c:3034
 do_mount fs/namespace.c:3377 [inline]
 __do_sys_mount fs/namespace.c:3585 [inline]
 __se_sys_mount+0x2e3/0x3d0 fs/namespace.c:3562
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Freed by task 4399:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 cifs_put_tcp_session+0x2e1/0x3d0 fs/cifs/connect.c:1404
 mount_put_conns+0xb0/0x270 fs/cifs/connect.c:2969
 cifs_mount+0xbf5/0x1380 fs/cifs/connect.c:3597
 cifs_smb3_do_mount+0x366/0x760 fs/cifs/cifsfs.c:895
 smb3_get_tree_common fs/cifs/fs_context.c:708 [inline]
 smb3_get_tree+0x59a/0xa80 fs/cifs/fs_context.c:726
 vfs_get_tree+0x88/0x270 fs/super.c:1530
 do_new_mount+0x247/0xa40 fs/namespace.c:3034
 do_mount fs/namespace.c:3377 [inline]
 __do_sys_mount fs/namespace.c:3585 [inline]
 __se_sys_mount+0x2e3/0x3d0 fs/namespace.c:3562
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff888071136260
 which belongs to the cache kmalloc-16 of size 16
The buggy address is located 0 bytes inside of
 16-byte region [ffff888071136260, ffff888071136270)
The buggy address belongs to the page:
page:ffffea0001c44d80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x71136
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000200 0000000000000000 dead000000000122 ffff888016c413c0
raw: 0000000000000000 0000000080800080 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x112cc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY), pid 4299, ts 89404424684, free_ts 89397043492
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x24f6/0x2670 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
 __alloc_pages_node include/linux/gfp.h:570 [inline]
 alloc_slab_page mm/slub.c:1782 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xb6/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x807/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 __kmalloc_node+0x142/0x3a0 mm/slub.c:4456
 kmalloc_node include/linux/slab.h:630 [inline]
 kvmalloc_node+0x84/0x130 mm/util.c:619
 xt_jumpstack_alloc net/netfilter/x_tables.c:1377 [inline]
 xt_replace_table+0x160/0x750 net/netfilter/x_tables.c:1416
 __do_replace+0x16f/0xa00 net/ipv6/netfilter/ip6_tables.c:1081
 do_replace net/ipv6/netfilter/ip6_tables.c:1158 [inline]
 do_ip6t_set_ctl+0xaa4/0xd90 net/ipv6/netfilter/ip6_tables.c:1643
 nf_setsockopt+0x25f/0x280 net/netfilter/nf_sockopt.c:101
 ipv6_setsockopt+0x20ba/0x3cc0 net/ipv6/ipv6_sockglue.c:1014
 tcp_setsockopt+0x229/0x1e60 net/ipv4/tcp.c:3722
 __sys_setsockopt+0x2bf/0x3d0 net/socket.c:2213
 __do_sys_setsockopt net/socket.c:2224 [inline]
 __se_sys_setsockopt net/socket.c:2221 [inline]
 __x64_sys_setsockopt+0xb1/0xc0 net/socket.c:2221
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x8f/0x2a0 mm/page_alloc.c:3396
 __vunmap+0x8e0/0xa80 mm/vmalloc.c:2628
 free_work+0x56/0x80 mm/vmalloc.c:95
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Memory state around the buggy address:
 ffff888071136100: 00 00 fc fc fa fb fc fc 00 00 fc fc 00 00 fc fc
 ffff888071136180: 00 00 fc fc fa fb fc fc 00 06 fc fc 00 00 fc fc
>ffff888071136200: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
                                                       ^
 ffff888071136280: 00 00 fc fc 00 00 fc fc fc fc fc fc fc fc fc fc
 ffff888071136300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (19):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/07 23:22 linux-5.15.y aabd761612db e4ef95d6 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/12 00:25 linux-5.15.y 0996e0926f6b b6a5eeb7 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/08/10 09:38 linux-5.15.y aabd761612db 5d63f80b .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/14 18:06 linux-5.15.y 0248c33e835e 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/14 08:48 linux-5.15.y 0996e0926f6b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/14 08:45 linux-5.15.y 0996e0926f6b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/14 08:44 linux-5.15.y 0996e0926f6b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/14 08:42 linux-5.15.y 0996e0926f6b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/14 08:37 linux-5.15.y 0996e0926f6b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/11 23:05 linux-5.15.y 0996e0926f6b b6a5eeb7 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/10 19:13 linux-5.15.y 0996e0926f6b 1fe56c0a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/10 03:50 linux-5.15.y 0996e0926f6b 4e8b1cc6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/09/04 02:31 linux-5.15.y 0996e0926f6b 801f0966 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/08/27 17:04 linux-5.15.y 4a1eaf96ee5c 69a01293 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/08/26 18:47 linux-5.15.y 945fa863f02c a2b77b9e .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/08/16 06:30 linux-5.15.y aabd761612db 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/08/12 21:35 linux-5.15.y aabd761612db 359b2492 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/08/08 09:20 linux-5.15.y aabd761612db 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
2026/08/07 16:20 linux-5.15.y aabd761612db e4ef95d6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in reconn_set_ipaddr_from_hostname
* Struck through repros no longer work on HEAD.