diff mbox series

[5.4,015/104] keys: Do not cache key in task struct if key is requested from kernel thread

Message ID 20230403140404.785142940@linuxfoundation.org (mailing list archive)
State New, archived
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman April 3, 2023, 2:08 p.m. UTC
From: David Howells <dhowells@redhat.com>

[ Upstream commit 47f9e4c924025c5be87959d3335e66fcbb7f6b5c ]

The key which gets cached in task structure from a kernel thread does not
get invalidated even after expiry.  Due to which, a new key request from
kernel thread will be served with the cached key if it's present in task
struct irrespective of the key validity.  The change is to not cache key in
task_struct when key requested from kernel thread so that kernel thread
gets a valid key on every key request.

The problem has been seen with the cifs module doing DNS lookups from a
kernel thread and the results getting pinned by being attached to that
kernel thread's cache - and thus not something that can be easily got rid
of.  The cache would ordinarily be cleared by notify-resume, but kernel
threads don't do that.

This isn't seen with AFS because AFS is doing request_key() within the
kernel half of a user thread - which will do notify-resume.

Fixes: 7743c48e54ee ("keys: Cache result of request_key*() temporarily in task_struct")
Signed-off-by: Bharath SM <bharathsm@microsoft.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Steve French <smfrench@gmail.com>
cc: keyrings@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/CAGypqWw951d=zYRbdgNR4snUDvJhWL=q3=WOyh7HhSJupjz2vA@mail.gmail.com/
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 security/keys/request_key.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
diff mbox series

Patch

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 957b9e3e14924..17c9c0cfb6f59 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -38,9 +38,12 @@  static void cache_requested_key(struct key *key)
 #ifdef CONFIG_KEYS_REQUEST_CACHE
 	struct task_struct *t = current;
 
-	key_put(t->cached_requested_key);
-	t->cached_requested_key = key_get(key);
-	set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
+	/* Do not cache key if it is a kernel thread */
+	if (!(t->flags & PF_KTHREAD)) {
+		key_put(t->cached_requested_key);
+		t->cached_requested_key = key_get(key);
+		set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
+	}
 #endif
 }