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[3/3] keys: Do not cache key in task struct if key is requested from kernel thread

Message ID 20230330182710.1141816-4-tim.gardner@canonical.com
State New
Headers show
Series Azure: smb3: allow deferred close timeout to be configurable | expand

Commit Message

Tim Gardner March 30, 2023, 6:27 p.m. UTC 
From: David Howells <dhowells@redhat.com>

BugLink: https://bugs.launchpad.net/bugs/2013349

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/
(cherry picked from commit 47f9e4c924025c5be87959d3335e66fcbb7f6b5c)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 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 2da4404276f0..07a0ef2baacd 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
 }