Hello, We found the following issue using syzkaller on Linux v6.11. In function `gsm_dlci_config`, a use-after-free on object `dlci` has been detected. Since the reproducer takes around 10 seconds to trigger the bug, it might be a race condition one. The C reproducer is available at:https://gist.github.com/TomAPU/2ef61db5e741daa2b4b040fd874b9e92#file-gsmvuln-c ================================================================== BUG: KASAN: slab-use-after-free in gsm_dlci_config+0x7b7/0x1020 drivers/tty/n_gsm.c:2588 Read of size 4 at addr ffff88803dab000c by task syz.0.361/12086 CPU: 0 PID: 12086 Comm: syz.0.361 Not tainted 6.10.0 #13 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x23d/0x360 lib/dump_stack.c:114 print_address_description+0x77/0x360 mm/kasan/report.c:377 print_report+0xfd/0x210 mm/kasan/report.c:488 kasan_report+0x13f/0x170 mm/kasan/report.c:601 gsm_dlci_config+0x7b7/0x1020 drivers/tty/n_gsm.c:2588 gsmld_ioctl+0xbbc/0x2540 drivers/tty/n_gsm.c:3880 tty_ioctl+0x98f/0xdb0 drivers/tty/tty_io.c:2812 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xfe/0x170 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x7e/0x150 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x67/0x6f RIP: 0033:0x7f86c25809b9 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:00007f86c3429038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f86c2745f80 RCX: 00007f86c25809b9 RDX: 0000000020000200 RSI: 0000000040384708 RDI: 0000000000000003 RBP: 00007f86c25f4f70 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007f86c2745f80 R15: 00007ffd81f1d488 </TASK> Allocated by task 12086: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3b/0x70 mm/kasan/common.c:68 poison_kmalloc_redzone mm/kasan/common.c:370 [inline] __kasan_kmalloc+0x94/0xa0 mm/kasan/common.c:387 kasan_kmalloc include/linux/kasan.h:211 [inline] kmalloc_trace_noprof+0x19e/0x2b0 mm/slub.c:4154 kmalloc_noprof include/linux/slab.h:660 [inline] kzalloc_noprof include/linux/slab.h:778 [inline] gsm_dlci_alloc+0x53/0x6c0 drivers/tty/n_gsm.c:2643 gsmld_ioctl+0xb99/0x2540 drivers/tty/n_gsm.c:3876 tty_ioctl+0x98f/0xdb0 drivers/tty/tty_io.c:2812 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xfe/0x170 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x7e/0x150 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x67/0x6f Freed by task 12087: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3b/0x70 mm/kasan/common.c:68 kasan_save_free_info+0x3c/0x50 mm/kasan/generic.c:579 poison_slab_object+0xe0/0x140 mm/kasan/common.c:240 __kasan_slab_free+0x33/0x50 mm/kasan/common.c:256 kasan_slab_free include/linux/kasan.h:184 [inline] slab_free_hook mm/slub.c:2196 [inline] slab_free mm/slub.c:4438 [inline] kfree+0x118/0x2a0 mm/slub.c:4559 dlci_put drivers/tty/n_gsm.c:2706 [inline] gsm_dlci_release drivers/tty/n_gsm.c:2739 [inline] gsm_cleanup_mux+0x5a2/0x930 drivers/tty/n_gsm.c:3156 gsm_config drivers/tty/n_gsm.c:3408 [inline] gsmld_ioctl+0x13c4/0x2540 drivers/tty/n_gsm.c:3839 tty_ioctl+0x98f/0xdb0 drivers/tty/tty_io.c:2812 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xfe/0x170 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x7e/0x150 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x67/0x6f The buggy address belongs to the object at ffff88803dab0000 which belongs to the cache kmalloc-2k of size 2048 The buggy address is located 12 bytes inside of freed 2048-byte region [ffff88803dab0000, ffff88803dab0800) The buggy address belongs to the physical page: page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x3dab0 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: 0xffffefff(slab) raw: 00fff00000000040 ffff888013042000 dead000000000100 dead000000000122 raw: 0000000000000000 0000000000080008 00000001ffffefff 0000000000000000 head: 00fff00000000040 ffff888013042000 dead000000000100 dead000000000122 head: 0000000000000000 0000000000080008 00000001ffffefff 0000000000000000 head: 00fff00000000003 ffffea0000f6ac01 ffffffffffffffff 0000000000000000 head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: kasan: bad access detected page_owner tracks the page as allocated page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 8050, tgid 8050 (syz-executor), ts 139463488880, free_ts 0 set_page_owner include/linux/page_owner.h:32 [inline] post_alloc_hook+0x1db/0x220 mm/page_alloc.c:1473 prep_new_page mm/page_alloc.c:1481 [inline] get_page_from_freelist+0x7e5/0x860 mm/page_alloc.c:3425 __alloc_pages_noprof+0x25a/0x580 mm/page_alloc.c:4683 __alloc_pages_node_noprof include/linux/gfp.h:269 [inline] alloc_pages_node_noprof include/linux/gfp.h:296 [inline] alloc_slab_page+0x67/0x130 mm/slub.c:2265 allocate_slab+0x5c/0x240 mm/slub.c:2428 new_slab mm/slub.c:2481 [inline] ___slab_alloc+0xc6b/0x10c0 mm/slub.c:3667 __slab_alloc+0x58/0xa0 mm/slub.c:3757 __slab_alloc_node mm/slub.c:3810 [inline] slab_alloc_node mm/slub.c:3990 [inline] __do_kmalloc_node mm/slub.c:4122 [inline] kmalloc_node_track_caller_noprof+0x268/0x410 mm/slub.c:4143 kmalloc_reserve+0x10e/0x2a0 net/core/skbuff.c:597 __alloc_skb+0x1e8/0x430 net/core/skbuff.c:666 alloc_skb include/linux/skbuff.h:1308 [inline] nlmsg_new include/net/netlink.h:1015 [inline] inet6_ifinfo_notify+0x6e/0x110 net/ipv6/addrconf.c:6161 addrconf_notify+0xca7/0x1000 net/ipv6/addrconf.c:3762 notifier_call_chain kernel/notifier.c:93 [inline] raw_notifier_call_chain+0xe0/0x180 kernel/notifier.c:461 __dev_notify_flags+0x201/0x400 dev_change_flags+0xe8/0x190 net/core/dev.c:8858 do_setlink+0xcc7/0x41e0 net/core/rtnetlink.c:2900 page_owner free stack trace missing Memory state around the buggy address: ffff88803daaff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88803daaff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff88803dab0000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88803dab0080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88803dab0100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================
