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Commit 437f7fdb authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

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: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarRoland McGrath <roland@redhat.com>
[ Fixed lock/unlock typo  - Hugh ]
Acked-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarLinus 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;