From: Vadim Lobanov <vlobanov@speakeasy.net>
To: Willy Tarreau <w@1wt.eu>
Subject: Re: [PATCH 2.4.33.2] enforce RLIMIT_NOFILE in poll()
Date: Thu, 31 Aug 2006 21:25:14 -0700
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Cc: Chris Snook <csnook@redhat.com>, linux-kernel@vger.kernel.org
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On Thursday 31 August 2006 20:48, Willy Tarreau wrote:
> Hi Chris,
>
> On Thu, Aug 31, 2006 at 09:06:55PM -0400, Chris Snook wrote:
> > From: Chris Snook <csnook@redhat.com>
> >
> > POSIX states that poll() shall fail with EINVAL if nfds > OPEN_MAX.  In
> > this context, POSIX is referring to sysconf(OPEN_MAX), which is the value
> > of current->rlim[RLIMIT_NOFILE].rlim_cur, not the compile-time constant
> > which happens to be named OPEN_MAX.  The current code will permit polling
> > up to 1024 file descriptors even if RLIMIT_NOFILE is less than 1024,
> > which POSIX forbids. The current code also breaks polling greater than
> > 1024 file descriptors if the process has less than 1024 valid
> > descriptors, even if RLIMIT_NOFILE > 1024.  While it is silly to poll
> > duplicate or invalid file descriptors, POSIX permits this, and it worked
> > circa 2.4.18, and currently works up to 1024. This patch directly checks
> > the RLIMIT_NOFILE value, and permits exactly what POSIX suggests, no
> > more, no less.
>
> While I understand that it was a bug before, I fear that it could break
> existing apps. Are you aware of some apps which do not work as expected
> because of this bug ? If not, I'd prefer to wait for some feedback from
> 2.6 with this fix before applying it (or maybe you're already using it
> in RHEL with success ?).

I submitted a similar but different patch for this very same issue against the 
2.6 kernel. It's currently residing in the -mm tree. Andrew Morton is 
somewhat reticent (and understandably so) to push it quickly into the vanilla 
tree; but, for what it's worth, I've yet to hear -- either directly or 
indirectly -- of any application breakages caused by this fix.

> Thanks,
> Willy
>
> > Signed-off-by: Chris Snook <csnook@redhat.com>
> > ---
> >
> > diff -urNp linux-2.4.33.2-orig/fs/select.c
> > linux-2.4.33.2-patch/fs/select.c ---
> > linux-2.4.33.2-orig/fs/select.c	2006-08-22 16:13:54.000000000 -0400 +++
> > linux-2.4.33.2-patch/fs/select.c	2006-08-31 13:43:39.000000000 -0400 @@
> > -417,7 +417,7 @@ asmlinkage long sys_poll(struct pollfd *
> >  	int nchunks, nleft;
> >
> >  	/* Do a sanity check on nfds ... */
> > -	if (nfds > current->files->max_fdset && nfds > OPEN_MAX)
> > +	if (nfds > current->rlim[RLIMIT_NOFILE].rlim_cur)
> >  		return -EINVAL;
> >
> >  	if (timeout) {
>

-- Vadim Lobanov
-
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