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    SubjectRe: [PATCH 2.4.33.2] enforce RLIMIT_NOFILE in poll()
    Date
    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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