Re: net/can: warning in bcm_connect/proc_register

Hi Cong,

I'm able to reproduce it by running
https://gist.github.com/xairy/33f2eb6bf807b004e643bae36c3d02d7 in a
tight parallel loop with stress
(https://godoc.org/golang.org/x/tools/cmd/stress):
$ gcc -lpthread tmp.c
$ ./stress ./a.out

The C program was generated from the following syzkaller prog:
mmap(&(0x7f0000000000/0x991000)=nil, (0x991000), 0x3, 0x32,
0xffffffffffffffff, 0x0)
socket(0x1d, 0x80002, 0x2)
r0 = socket(0x1d, 0x80002, 0x2)
connect$nfc_llcp(r0, &(0x7f000000c000)={0x27, 0x100000000, 0x0, 0x5,
0x100000000, 0x1,
"341b3a01b257849ca1d7d1ff9f999d8127b185f88d1d775d59c88a3aa6a8ddacdf2bdc324ea6578a21b85114610186c3817c34b05eaffd2c3f54f57fa81ba0",
0x1ff}, 0x60)
connect$nfc_llcp(r0, &(0x7f0000991000-0x60)={0x27, 0x100000000, 0x1,
0x5, 0xfffffffffffffffd, 0x0,
"341b3a01b257849ca1d7d1ff9f999d8127b185f88d1d775dbec88a3aa6a8ddacdf2bdc324ea6578a21b85114610186c3817c34b05eaffd2c3f54f57fa81ba0",
0x1ff}, 0x60)

Unfortunately I wasn't able to create a simpler reproducer.

Thanks!

On Mon, Oct 24, 2016 at 6:58 PM, Cong Wang [off-list ref] wrote:

On Mon, Oct 24, 2016 at 9:21 AM, Andrey Konovalov [off-list ref] wrote:

quoted

Hi,

I've got the following error report while running the syzkaller fuzzer:

WARNING: CPU: 0 PID: 32451 at fs/proc/generic.c:345 proc_register+0x25e/0x300
proc_dir_entry 'can-bcm/249757' already registered
Kernel panic - not syncing: panic_on_warn set ...

Looks like we have two problems here:

1) A check for bo->bcm_proc_read != NULL seems missing
2) We need to lock the sock in bcm_connect().

I will work on a patch. Meanwhile, it would help a lot if you could provide
a reproducer.

Thanks!