Re: [syzbot] [can?] WARNING in remove_proc_entry (6)

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: syzbot <syzbot+0532ac7a06fb1a03187e@syzkaller.appspotmail.com>
Date: Wed, 04 Sep 2024 06:56:23 -0700
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    5517ae241919 Merge tag 'for-net-2024-08-30' of git://git.k..
> git tree:       net
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=111adcfb980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=996585887acdadb3
> dashboard link: https://syzkaller.appspot.com/bug?extid=0532ac7a06fb1a03187e
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=138d43db980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11fe3d43980000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/ddded5c54678/disk-5517ae24.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/ce0dfe9dbb55/vmlinux-5517ae24.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/ca81d6e3361d/bzImage-5517ae24.xz
> 
> The issue was bisected to:
> 
> commit 76fe372ccb81b0c89b6cd2fec26e2f38c958be85
> Author: Kuniyuki Iwashima <kuniyu@amazon.com>
> Date:   Mon Jul 22 19:28:42 2024 +0000
> 
>     can: bcm: Remove proc entry when dev is unregistered.
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=116f8e8f980000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=136f8e8f980000
> console output: https://syzkaller.appspot.com/x/log.txt?x=156f8e8f980000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+0532ac7a06fb1a03187e@syzkaller.appspotmail.com
> Fixes: 76fe372ccb81 ("can: bcm: Remove proc entry when dev is unregistered.")
> 
> ------------[ cut here ]------------
> name '4986'
> WARNING: CPU: 0 PID: 5234 at fs/proc/generic.c:711 remove_proc_entry+0x2e7/0x5d0 fs/proc/generic.c:711
> Modules linked in:
> CPU: 0 UID: 0 PID: 5234 Comm: syz-executor606 Not tainted 6.11.0-rc5-syzkaller-00178-g5517ae241919 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
> RIP: 0010:remove_proc_entry+0x2e7/0x5d0 fs/proc/generic.c:711
> Code: ff eb 05 e8 cb 1e 5e ff 48 8b 5c 24 10 48 c7 c7 e0 f7 aa 8e e8 2a 38 8e 09 90 48 c7 c7 60 3a 1b 8c 48 89 de e8 da 42 20 ff 90 <0f> 0b 90 90 48 8b 44 24 18 48 c7 44 24 40 0e 36 e0 45 49 c7 04 07
> RSP: 0018:ffffc9000345fa20 EFLAGS: 00010246
> RAX: 2a2d0aee2eb64600 RBX: ffff888032f1f548 RCX: ffff888029431e00
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: ffffc9000345fb08 R08: ffffffff8155b2f2 R09: 1ffff1101710519a
> R10: dffffc0000000000 R11: ffffed101710519b R12: ffff888011d38640
> R13: 0000000000000004 R14: 0000000000000000 R15: dffffc0000000000
> FS:  0000000000000000(0000) GS:ffff8880b8800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fcfb52722f0 CR3: 000000000e734000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  bcm_release+0x250/0x880 net/can/bcm.c:1578
>  __sock_release net/socket.c:659 [inline]
>  sock_close+0xbc/0x240 net/socket.c:1421
>  __fput+0x24a/0x8a0 fs/file_table.c:422
>  task_work_run+0x24f/0x310 kernel/task_work.c:228
>  exit_task_work include/linux/task_work.h:40 [inline]
>  do_exit+0xa2f/0x27f0 kernel/exit.c:882
>  do_group_exit+0x207/0x2c0 kernel/exit.c:1031
>  __do_sys_exit_group kernel/exit.c:1042 [inline]
>  __se_sys_exit_group kernel/exit.c:1040 [inline]
>  __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1040
>  x64_sys_call+0x2634/0x2640 arch/x86/include/generated/asm/syscalls_64.h:232
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fcfb51ee969
> Code: Unable to access opcode bytes at 0x7fcfb51ee93f.
> RSP: 002b:00007ffce0109ca8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fcfb51ee969
> RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000001
> RBP: 00007fcfb526f3b0 R08: ffffffffffffffb8 R09: 0000555500000000
> R10: 0000555500000000 R11: 0000000000000246 R12: 00007fcfb526f3b0
> R13: 0000000000000000 R14: 00007fcfb5271ee0 R15: 00007fcfb51bf160
>  </TASK>
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash

Ugh, I forgot to clear bo->bcm_proc_read.

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git HEAD

diff --git a/net/can/bcm.c b/net/can/bcm.c
index 46d3ec3aa44b..217049fa496e 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1471,8 +1471,10 @@ static void bcm_notify(struct bcm_sock *bo, unsigned long msg,
 		/* remove device reference, if this is our bound device */
 		if (bo->bound && bo->ifindex == dev->ifindex) {
 #if IS_ENABLED(CONFIG_PROC_FS)
-			if (sock_net(sk)->can.bcmproc_dir && bo->bcm_proc_read)
+			if (sock_net(sk)->can.bcmproc_dir && bo->bcm_proc_read) {
 				remove_proc_entry(bo->procname, sock_net(sk)->can.bcmproc_dir);
+				bo->bcm_proc_read = NULL;
+			}
 #endif
 			bo->bound   = 0;
 			bo->ifindex = 0;