[syzbot] [nvme?] kernel BUG in nvmet_fc_remove_port

[Hillf Danton]

> Date: Tue, 27 Oct 2026 05:08:55 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    6b4b543fa187 Merge tag 'parisc-for-7.4-rc1' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16ce8f0d580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b4c032ed87e6e91c
> dashboard link: https://syzkaller.appspot.com/bug?extid=df0058a8d0bdce7c4059
> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17db5e35580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1413f195580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-6b4b543f.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/003ef0d7eda6/vmlinux-6b4b543f.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/022618083bf9/bzImage-6b4b543f.xz
> 
> AI-generated root cause summary:
> In the NVMe target subsystem, port attribute store handlers in
> drivers/nvme/target/configfs.c (such as nvmet_addr_trtype_store) do not acquire
> nvmet_config_sem and only check port->enabled. Because port->enabled is not set
> to true until after ops->add_port() finishes in nvmet_enable_port(), a
> concurrent write to addr_trtype can race and switch port->disc_addr.trtype
> (e.g., from TCP to FC). When disabling the port, nvmet_disable_port() in
> drivers/nvme/target/core.c indexes nvmet_transports using port->disc_addr.trtype
> instead of using port->tr_ops, causing type confusion on port->priv (treating
> struct nvmet_tcp_port as struct nvmet_fc_port_entry) and resulting in memory
> corruption, refcount underflow, and use-after-free.
> 
Sounds incorrect given the debug diff that survived a similar syzbot test [11].

[11] https://lore.kernel.org/lkml/6ad48c36.a6d1a155.34a93f.0091.GAE@google.com/

> full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=df0058a8d0bdce7c4059
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+df0058a8d0bdce7c4059 at syzkaller.appspotmail.com
> 
> nvmet_tcp: enabling port 1 (127.0.0.1:4420)
> refcount_t: underflow; use-after-free.
> ------------[ cut here ]------------
> kernel BUG at lib/refcount.c:37!
> Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
> CPU: 0 UID: 0 PID: 6113 Comm: syz.0.43 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> RIP: 0010:refcount_warn_saturate+0xd7/0x110 lib/refcount.c:37
> Code: 67 48 0f b9 3a e8 b9 e8 d6 fc 5b 5d e9 c2 d6 b5 06 77 19 83 fd 02 74 3e e8 a6 e8 d6 fc 48 c7 c7 c0 08 81 8c e8 ba 43 eb fb 90 <0f> 0b e8 92 e8 d6 fc 48 8d 3d 6b 27 3d 0d 67 48 0f b9 3a e8 81 e8
> RSP: 0018:ffffc900039d7c00 EFLAGS: 00010086
> RAX: 0000000000000026 RBX: ffff8880549e4678 RCX: 0000000000000000
> RDX: 0000000000000026 RSI: ffffffff81ebe399 RDI: fffff5200073af71
> RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000001 R12: 1ffff9200073af85
> R13: 0000000000000000 R14: 0000000000000000 R15: ffff8880549e4678
> FS:  0000555566238500(0000) GS:ffff8880d449e000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f8d01471220 CR3: 000000002d14f000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  __refcount_sub_and_test include/linux/refcount.h:400 [inline]
>  __refcount_dec_and_test include/linux/refcount.h:432 [inline]
>  refcount_dec_and_test include/linux/refcount.h:450 [inline]
>  kref_put include/linux/kref.h:64 [inline]
>  nvmet_fc_tgtport_put drivers/nvme/target/fc.c:1464 [inline]
>  nvmet_fc_portentry_unbind drivers/nvme/target/fc.c:1278 [inline]
>  nvmet_fc_remove_port+0x4c2/0x5f0 drivers/nvme/target/fc.c:2930
>  nvmet_disable_port+0x13c/0x200 drivers/nvme/target/core.c:400
>  nvmet_port_subsys_drop_link+0x26b/0x310 drivers/nvme/target/configfs.c:1189
>  configfs_unlink+0x3cc/0x800 fs/configfs/symlink.c:258
>  vfs_unlink+0x2f0/0xbd0 fs/namei.c:5661
>  filename_unlinkat+0x408/0x730 fs/namei.c:5731
>  __do_sys_unlinkat fs/namei.c:5760 [inline]
>  __se_sys_unlinkat fs/namei.c:5752 [inline]
>  __x64_sys_unlinkat+0xc0/0x130 fs/namei.c:5752
>  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
>  do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f