From: Oleg Nesterov <oleg@redhat.com>
To: Hugh Dickins <hugh@veritas.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Joe Malicki <jmalicki@metacarta.com>,
Michael Itz <mitz@metacarta.com>,
Kenneth Baker <bakerk@metacarta.com>,
Chris Wright <chrisw@sous-sol.org>,
David Howells <dhowells@redhat.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Greg Kroah-Hartman <gregkh@suse.de>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Q: check_unsafe_exec() races (Was: [PATCH 2/4] fix setuid sometimes doesn't)
Date: Sun, 29 Mar 2009 01:53:43 +0100 [thread overview]
Message-ID: <20090329005343.GA12139@redhat.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0903282319270.15432@blonde.anvils>
> -void check_unsafe_exec(struct linux_binprm *bprm, struct files_struct *files)
> +void check_unsafe_exec(struct linux_binprm *bprm)
> {
> struct task_struct *p = current, *t;
> unsigned long flags;
> - unsigned n_fs, n_files, n_sighand;
> + unsigned n_fs, n_sighand;
>
> bprm->unsafe = tracehook_unsafe_exec(p);
>
> n_fs = 1;
> - n_files = 1;
> n_sighand = 1;
> lock_task_sighand(p, &flags);
> for (t = next_thread(p); t != p; t = next_thread(t)) {
> if (t->fs == p->fs)
> n_fs++;
> - if (t->files == files)
> - n_files++;
> n_sighand++;
> }
>
> if (atomic_read(&p->fs->count) > n_fs ||
> - atomic_read(&p->files->count) > n_files ||
> atomic_read(&p->sighand->count) > n_sighand)
> bprm->unsafe |= LSM_UNSAFE_SHARE;
Can't find the patch which introduced check_unsafe_exec(), so
I am asking here.
How it is supposed to work?
Let's suppose we have two threads T1 and T2. T1 exits, and calls
exit_fs().
exit_fs:
tsk->fs = NULL;
// WINDOW
put_fs_struct(fs);
Now, if T2 does exec() and check_unsafe_exec() happens in the WINDOW
above, we set LSM_UNSAFE_SHARE.
Or we can race with sub-thread doing clone(CLONE_FS|CLONE_THREAD),
the new thread is not visible in ->thread_group, buy copy_fs()
can already increment fs->count.
Another question. Why do we check sighand->count? We always unshare
->sighand on exec, see de_thread().
Minor, but why lock_task_sighand() ? This helper is "__must_check".
If it can't fail (yes, it can't fail here), spin_lock_irq(siglock)
is enough. (and given that ->siglock can't help anyway to calculate
n_fs, we could use rcu_read_lock() instead).
(as for these patches, I think they are correct).
Oleg.
next prev parent reply other threads:[~2009-03-29 0:59 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-28 23:16 [PATCH 1/4] compat_do_execve should unshare_files Hugh Dickins
2009-03-28 23:20 ` [PATCH 2/4] fix setuid sometimes doesn't Hugh Dickins
2009-03-29 0:53 ` Oleg Nesterov [this message]
2009-03-29 4:10 ` Q: check_unsafe_exec() races (Was: [PATCH 2/4] fix setuid sometimes doesn't) Al Viro
2009-03-29 4:14 ` Al Viro
2009-03-29 4:52 ` Oleg Nesterov
2009-03-29 5:55 ` Al Viro
2009-03-29 6:01 ` Al Viro
2009-03-29 21:36 ` Oleg Nesterov
2009-03-29 22:20 ` Al Viro
2009-03-29 23:56 ` Oleg Nesterov
2009-03-30 0:03 ` Oleg Nesterov
2009-03-30 1:08 ` Al Viro
2009-03-30 1:13 ` Al Viro
2009-03-30 1:36 ` Oleg Nesterov
2009-03-30 1:40 ` Oleg Nesterov
2009-03-30 12:31 ` Al Viro
2009-03-30 14:32 ` Hugh Dickins
2009-03-31 6:16 ` Al Viro
2009-04-01 0:28 ` Hugh Dickins
2009-04-01 2:38 ` Al Viro
2009-04-01 3:03 ` Al Viro
2009-04-01 11:25 ` Hugh Dickins
2009-04-06 15:31 ` Oleg Nesterov
2009-04-19 16:30 ` Hugh Dickins
2009-04-21 16:10 ` Oleg Nesterov
2009-04-21 16:31 ` Linus Torvalds
2009-04-21 17:15 ` Oleg Nesterov
2009-04-21 17:35 ` Linus Torvalds
2009-04-21 19:39 ` Hugh Dickins
2009-04-23 23:01 ` [PATCH 1/2] do_execve() must not clear fs->in_exec if it was set by another thread Oleg Nesterov
2009-04-23 23:18 ` Roland McGrath
2009-04-23 23:31 ` Al Viro
2009-04-24 11:57 ` [PATCH 3/2] check_unsafe_exec: rcu_read_unlock Hugh Dickins
2009-04-24 14:34 ` Oleg Nesterov
2009-04-24 4:20 ` [PATCH 1/2] do_execve() must not clear fs->in_exec if it was set by another thread Hugh Dickins
2009-04-23 23:02 ` [PATCH 2/2] check_unsafe_exec: s/lock_task_sighand/rcu_read_lock/ Oleg Nesterov
2009-04-23 23:18 ` Roland McGrath
2009-04-24 4:29 ` Hugh Dickins
2009-04-01 11:18 ` Q: check_unsafe_exec() races (Was: [PATCH 2/4] fix setuid sometimes doesn't) Hugh Dickins
2009-04-06 15:51 ` Oleg Nesterov
2009-04-19 16:44 ` Hugh Dickins
2009-04-21 16:39 ` Oleg Nesterov
2009-03-30 23:45 ` Serge E. Hallyn
2009-03-31 6:19 ` Al Viro
2009-03-28 23:21 ` [PATCH 3/4] fix setuid sometimes wouldn't Hugh Dickins
2009-03-29 11:19 ` Alexey Dobriyan
2009-03-29 21:48 ` Oleg Nesterov
2009-03-29 22:37 ` Al Viro
2009-03-28 23:23 ` [PATCH 4/4] Annotate struct fs_struct's usage count restriction Hugh Dickins
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