Re: net: BUG in unix_notinflight

On Tue, Mar 7, 2017 at 2:23 PM, Nikolay Borisov
[off-list ref] wrote:

quoted

quoted

New report from linux-next/c0b7b2b33bd17f7155956d0338ce92615da686c9

------------[ cut here ]------------
kernel BUG at net/unix/garbage.c:149!
invalid opcode: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 1806 Comm: syz-executor7 Not tainted 4.10.0-next-20170303+ #6
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
task: ffff880121c64740 task.stack: ffff88012c9e8000
RIP: 0010:unix_notinflight+0x417/0x5d0 net/unix/garbage.c:149
RSP: 0018:ffff88012c9ef0f8 EFLAGS: 00010297
RAX: ffff880121c64740 RBX: 1ffff1002593de23 RCX: ffff8801c490c628
RDX: 0000000000000000 RSI: 1ffff1002593de27 RDI: ffffffff8557e504
RBP: ffff88012c9ef220 R08: 0000000000000001 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed002593de55 R12: ffff8801c490c0c0
R13: ffff88012c9ef1f8 R14: ffffffff85101620 R15: dffffc0000000000
FS:  00000000013d3940(0000) GS:ffff8801dbe00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001fd8cd8 CR3: 00000001cce69000 CR4: 00000000001426f0
Call Trace:
 unix_detach_fds.isra.23+0xfa/0x170 net/unix/af_unix.c:1490
 unix_destruct_scm+0xf4/0x200 net/unix/af_unix.c:1499

The problem here is there is no lock protecting concurrent unix_detach_fds()
even though unix_notinflight() is already serialized, if we call
unix_notinflight()
twice on the same file pointer, we trigger this bug...

I don't know what is the right lock here to serialize it.

I reported something similar a while ago
https://lists.gt.net/linux/kernel/2534612

And Miklos Szeredi then produced the following patch :

https://patchwork.kernel.org/patch/9305121/

However, this was never applied. I wonder if the patch makes sense?

I doubt it is the same case. According to Miklos' description,
the case he tried to fix is MSG_PEEK, but Dmitry's test case does not
set it... They are different problems probably.