[PATCH 5.4 084/203] keys: Fix request_key() cache

Greg Kroah-Hartman
2020-01-16T23:45:50Z

From: David Howells <dhowells@redhat.com>

commit 8379bb84be757d5df2d818509faec5d66adb861d upstream.

When the key cached by request_key() and co. is cleaned up on exit(),
the code looks in the wrong task_struct, and so clears the wrong cache.
This leads to anomalies in key refcounting when doing, say, a kernel
build on an afs volume, that then trigger kasan to report a
use-after-free when the key is viewed in /proc/keys.

Fix this by making exit_creds() look in the passed-in task_struct rather
than in current (the task_struct cleanup code is deferred by RCU and
potentially run in another task).

Fixes: 7743c48e54ee ("keys: Cache result of request_key*() temporarily in task_struct")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/cred.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -175,8 +175,8 @@ void exit_creds(struct task_struct *tsk)
put_cred(cred);

#ifdef CONFIG_KEYS_REQUEST_CACHE
- key_put(current->cached_requested_key);
- current->cached_requested_key = NULL;
+ key_put(tsk->cached_requested_key);
+ tsk->cached_requested_key = NULL;
#endif
}