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check_unsafe_exec: s/lock_task_sighand/rcu_read_lock/

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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>
This commit is contained in:
Oleg Nesterov 2009-04-24 01:02:45 +02:00 committed by Linus Torvalds
parent 8c652f96d3
commit 437f7fdb60
1 changed files with 2 additions and 4 deletions
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6
fs/exec.c
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@ -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;