CRED: Use RCU to access another task's creds and to release a task's own creds
Use RCU to access another task's creds and to release a task's own creds.
This means that it will be possible for the credentials of a task to be
replaced without another task (a) requiring a full lock to read them, and (b)
seeing deallocated memory.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/fs/fcntl.c b/fs/fcntl.c
index c594cc0..87c39f1 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -401,10 +401,17 @@
static inline int sigio_perm(struct task_struct *p,
struct fown_struct *fown, int sig)
{
- return (((fown->euid == 0) ||
- (fown->euid == p->cred->suid) || (fown->euid == p->cred->uid) ||
- (fown->uid == p->cred->suid) || (fown->uid == p->cred->uid)) &&
- !security_file_send_sigiotask(p, fown, sig));
+ const struct cred *cred;
+ int ret;
+
+ rcu_read_lock();
+ cred = __task_cred(p);
+ ret = ((fown->euid == 0 ||
+ fown->euid == cred->suid || fown->euid == cred->uid ||
+ fown->uid == cred->suid || fown->uid == cred->uid) &&
+ !security_file_send_sigiotask(p, fown, sig));
+ rcu_read_unlock();
+ return ret;
}
static void send_sigio_to_task(struct task_struct *p,