Re: [PATCH] UNIX: Do not loop forever at unix_autobind().

[David Miller <davem@davemloft.net>]

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 04 Sep 2010 20:34:28 +0900

> Subject: [PATCH] UNIX: Do not loop forever at unix_autobind().
> 
> We assumed that unix_autobind() never fails if kzalloc() succeeded.
> But unix_autobind() allows only 1048576 names. If /proc/sys/fs/file-max is
> larger than 1048576 (e.g. systems with more than 10GB of RAM), a local user can
> consume all names using fork()/socket()/bind().
> 
> If all names are in use, those who call bind() with addr_len == sizeof(short)
> or connect()/sendmsg() with setsockopt(SO_PASSCRED) will continue
> 
>   while (1)
>         yield();
> 
> loop at unix_autobind() till a name becomes available.
> This patch adds a loop counter in order to give up after 1048576 attempts.
> 
> Calling yield() for once per 256 attempts may not be sufficient when many names
> are already in use, for __unix_find_socket_byname() can take long time under
> such circumstance. Therefore, this patch also adds cond_resched() call.
> 
> Note that currently a local user can consume 2GB of kernel memory if the user
> is allowed to create and autobind 1048576 UNIX domain sockets. We should
> consider adding some restriction for autobind operation.
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

Applied and queued up for -stable, thanks!