[PATCH 2/2] check_unsafe_exec: s/lock_task_sighand/rcu_read_lock/

Oleg Nesterov
2009-04-23T23:09:21Z

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>

--- PTRACE/fs/exec.c~2_NO_SIGLOCK 2009-04-24 00:01:53.000000000 +0200
+++ PTRACE/fs/exec.c 2009-04-24 00:36:22.000000000 +0200
@@ -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_binpr

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_lock();

if (p->fs->users > n_fs) {
bprm->unsafe |= LSM_UNSAFE_SHARE;
@@ -1083,8 +1083,6 @@ int check_unsafe_exec(struct linux_binpr
res = 1;
}
}
-
- unlock_task_sighand(p, &flags);
write_unlock(&p->fs->lock);

return res;