Commit 437f7fdb authored Apr 24, 2009 by Oleg Nesterov Committed by Linus Torvalds Apr 24, 2009

check_unsafe_exec: s/lock_task_sighand/rcu_read_lock/



write_lock(&current->fs->lock) guarantees we can't wrongly miss
LSM_UNSAFE_SHARE, this is what we care about. Use rcu_read_lock()
instead of ->siglock to iterate over the sub-threads. We must see
all CLONE_THREAD|CLONE_FS threads which didn't pass exit_fs(), it
takes fs->lock too.

With or without this patch we can miss the freshly cloned thread
and set LSM_UNSAFE_SHARE, we don't care.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
[ Fixed lock/unlock typo  - Hugh ]
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 8c652f96

fs/exec.c

+2 −4

Original line number	Diff line number	Diff line
		@@ -1060,7 +1060,6 @@ EXPORT_SYMBOL(install_exec_creds);
		int check_unsafe_exec(struct linux_binprm *bprm)
		{
		struct task_struct p = current, t;
		unsigned long flags;
		unsigned n_fs;
		int res = 0;

		@@ -1068,11 +1067,12 @@ int check_unsafe_exec(struct linux_binprm *bprm)

		n_fs = 1;
		write_lock(&p->fs->lock);
		lock_task_sighand(p, &flags);
		rcu_read_lock();
		for (t = next_thread(p); t != p; t = next_thread(t)) {
		if (t->fs == p->fs)
		n_fs++;
		}
		rcu_read_unlock();

		if (p->fs->users > n_fs) {
		bprm->unsafe \|= LSM_UNSAFE_SHARE;
		@@ -1083,8 +1083,6 @@ int check_unsafe_exec(struct linux_binprm *bprm)
		res = 1;
		}
		}

		unlock_task_sighand(p, &flags);
		write_unlock(&p->fs->lock);

		return res;

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