Re: memory leak in io_submit_sqes

From: Jens Axboe <axboe@kernel.dk>
To: syzbot <syzbot+a730016dc0bdce4f6ff5@syzkaller.appspotmail.com>,
	io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
	viro@zeniv.linux.org.uk
Subject: Re: memory leak in io_submit_sqes
Date: Tue, 11 Aug 2020 08:59:03 -0600	[thread overview]
Message-ID: <b8c5db23-c3cf-7daf-6a0a-8a5f713e9803@kernel.dk> (raw)
In-Reply-To: <000000000000f50fb505ac9a72c9@google.com>

On 8/11/20 7:57 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    d6efb3ac Merge tag 'tty-5.9-rc1' of git://git.kernel.org/p..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13cb0762900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=42163327839348a9
> dashboard link: https://syzkaller.appspot.com/bug?extid=a730016dc0bdce4f6ff5
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16e877dc900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1608291a900000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a730016dc0bdce4f6ff5@syzkaller.appspotmail.com
> 
> executing program
> executing program
> executing program
> executing program
> executing program
> BUG: memory leak
> unreferenced object 0xffff888124949100 (size 256):
>   comm "syz-executor808", pid 6480, jiffies 4294949911 (age 33.960s)
>   hex dump (first 32 bytes):
>     00 78 74 2a 81 88 ff ff 00 00 00 00 00 00 00 00  .xt*............
>     90 b0 51 81 ff ff ff ff 00 00 00 00 00 00 00 00  ..Q.............
>   backtrace:
>     [<0000000084e46f34>] io_alloc_req fs/io_uring.c:1503 [inline]
>     [<0000000084e46f34>] io_submit_sqes+0x5dc/0xc00 fs/io_uring.c:6306
>     [<000000006d4e19eb>] __do_sys_io_uring_enter+0x582/0x830 fs/io_uring.c:8036
>     [<00000000a4116b07>] do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>     [<0000000067b2aefc>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> BUG: memory leak
> unreferenced object 0xffff88811751d200 (size 96):
>   comm "syz-executor808", pid 6480, jiffies 4294949911 (age 33.960s)
>   hex dump (first 32 bytes):
>     00 78 74 2a 81 88 ff ff 00 00 00 00 00 00 00 00  .xt*............
>     0e 01 00 00 00 00 75 22 00 00 00 00 00 0f 1f 04  ......u"........
>   backtrace:
>     [<00000000073ea2ba>] kmalloc include/linux/slab.h:555 [inline]
>     [<00000000073ea2ba>] io_arm_poll_handler fs/io_uring.c:4773 [inline]
>     [<00000000073ea2ba>] __io_queue_sqe+0x445/0x6b0 fs/io_uring.c:5988
>     [<000000001551bde0>] io_queue_sqe+0x309/0x550 fs/io_uring.c:6060
>     [<000000002dfb908f>] io_submit_sqe fs/io_uring.c:6130 [inline]
>     [<000000002dfb908f>] io_submit_sqes+0x8b8/0xc00 fs/io_uring.c:6327
>     [<000000006d4e19eb>] __do_sys_io_uring_enter+0x582/0x830 fs/io_uring.c:8036
>     [<00000000a4116b07>] do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>     [<0000000067b2aefc>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

This one looks very odd, and I cannot reproduce it. The socket() calls
reliably fails for me, and even if I hack it to use 0 for protocol instead
of 2, I don't see anything interesting happening here. An IORING_OP_WRITEV
is submitted on the socket, which just fails with ENOTCONN.

-- 
Jens Axboe