Since we are going to adopt libmount for mount.nfs in the near future, would it be better to update libmount instead?
On Jun 22, 2011, at 12:38 AM, NeilBrown wrote:
>
> From: Neil Brown <neilb@xxxxxxx>
> Date: Wed, 22 Jun 2011 16:15:45 +1000
> Subject: [PATCH] mount: improve signal management when locking mtab.
>
> As mount.nfs can run setuid it must be careful about how the user can
> interact with in. In particular it needs to ensure it does not
> respond badly to any signals that the user might be able to generate.
>
> This is particularly an issue while updating /etc/mtab (when that is
> not linked to /proc/mounts). If the user can generate a signal which
> kills mount.nfs while /etc/mtab is locked, then it will leave the file
> locked, and could possibly corrupt mtab (particularly if 'ulimit 1'
> was previously issued).
>
> Currently lock_mtab does set some handlers for signals, but not
> enough. It arranges for every signal up to (but not including)
> SIGCHLD to cause mount.nfs to unlock mdadm promptly exit ... even if
> the default behaviour would be to ignore the signal. SIGALRM is
> handled specially, and signals after SIGCHLD are left with their
> default behaviour. This includes for example SIGXFSZ which can be
> generated by the user running "ulimit 1".
>
> So: change this so that some signals are left unchanged, SIGALRM is
> handled as required, and all signals that the user can generate are
> explicitly ignored.
>
> The remainder still cause mount.nfs to print a message, unlock mtab, and exit.
>
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> utils/mount/fstab.c | 37 ++++++++++++++++++++++++++++++++-----
> 1 files changed, 32 insertions(+), 5 deletions(-)
>
> diff --git a/utils/mount/fstab.c b/utils/mount/fstab.c
> index a742e64..1fc9efe 100644
> --- a/utils/mount/fstab.c
> +++ b/utils/mount/fstab.c
> @@ -331,16 +331,43 @@ lock_mtab (void) {
> int sig = 0;
> struct sigaction sa;
>
> - sa.sa_handler = handler;
> sa.sa_flags = 0;
> sigfillset (&sa.sa_mask);
>
> - while (sigismember (&sa.sa_mask, ++sig) != -1
> - && sig != SIGCHLD) {
> - if (sig == SIGALRM)
> + while (sigismember (&sa.sa_mask, ++sig) != -1) {
> + switch(sig) {
> + case SIGCHLD:
> + case SIGKILL:
> + case SIGCONT:
> + case SIGSTOP:
> + /* The cannot be caught, or should not,
> + * so don't even try.
> + */
> + continue;
> + case SIGALRM:
> sa.sa_handler = setlkw_timeout;
> - else
> + break;
> + case SIGHUP:
> + case SIGINT:
> + case SIGQUIT:
> + case SIGWINCH:
> + case SIGTSTP:
> + case SIGTTIN:
> + case SIGTTOU:
> + case SIGPIPE:
> + case SIGXFSZ:
> + case SIGXCPU:
> + /* non-priv user can cause these to be
> + * generated, so ignore them.
> + */
> + sa.sa_handler = SIG_IGN;
> + break;
> + default:
> + /* The rest should not be possible, so just
> + * print a message and unlock mtab.
> + */
> sa.sa_handler = handler;
> + }
> sigaction (sig, &sa, (struct sigaction *) 0);
> }
> signals_have_been_setup = 1;
> --
> 1.7.3.4
>
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--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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