From: David Howells <dhowells@redhat.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: dhowells@redhat.com, Kees Cook <kees@kernel.org>,
Greg KH <gregkh@linuxfoundation.org>,
Josh Drake <josh@delphoslabs.com>,
Suraj Sonawane <surajsonawane0215@gmail.com>,
keyrings@vger.kernel.org, linux-security-module@vger.kernel.org,
security@kernel.org, stable@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [PATCH] keys: Fix UAF in key_put()
Date: Tue, 18 Mar 2025 10:14:45 +0000 [thread overview]
Message-ID: <2477454.1742292885@warthog.procyon.org.uk> (raw)
From: Hillf Danton <hdanton@sina.com>
Once a key's reference count has been reduced to 0, the garbage collector
thread may destroy it at any time and so key_put() is not allowed to touch
the key after that point. The most key_put() is normally allowed to do is
to touch key_gc_work as that's a static global variable.
However, in an effort to speed up the reclamation of quota, this is now
done in key_put() once the key's usage is reduced to 0 - but now the code
is looking at the key after the deadline, which is forbidden.
Fix this on an expedited basis[*] by taking a ref on the key->user struct
and caching the key length before dropping the refcount so that we can
reduce the quota afterwards if we dropped the last ref.
[*] This is going to hurt key_put() performance, so a better way is
probably necessary, such as sticking the dead key onto a queue for the
garbage collector to pick up rather than having it scan the serial number
registry.
Fixes: 9578e327b2b4 ("keys: update key quotas in key_put()")
Reported-by: syzbot+6105ffc1ded71d194d6d@syzkaller.appspotmail.com
Tested-by: syzbot+6105ffc1ded71d194d6d@syzkaller.appspotmail.com
Suggested-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jarkko Sakkinen <jarkko@kernel.org>
cc: Kees Cook <kees@kernel.org>
cc: keyrings@vger.kernel.org
cc: stable@vger.kernel.org # v6.10+
---
security/keys/key.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/security/keys/key.c b/security/keys/key.c
index 3d7d185019d3..1e6028492355 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -645,21 +645,30 @@ EXPORT_SYMBOL(key_reject_and_link);
*/
void key_put(struct key *key)
{
+ int quota_flag;
+ unsigned short len;
+ struct key_user *user;
+
if (key) {
key_check(key);
+ quota_flag = test_bit(KEY_FLAG_IN_QUOTA, &key->flags);
+ len = key->quotalen;
+ user = key->user;
+ refcount_inc(&user->usage);
if (refcount_dec_and_test(&key->usage)) {
unsigned long flags;
/* deal with the user's key tracking and quota */
- if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
- spin_lock_irqsave(&key->user->lock, flags);
- key->user->qnkeys--;
- key->user->qnbytes -= key->quotalen;
- spin_unlock_irqrestore(&key->user->lock, flags);
+ if (quota_flag) {
+ spin_lock_irqsave(&user->lock, flags);
+ user->qnkeys--;
+ user->qnbytes -= len;
+ spin_unlock_irqrestore(&user->lock, flags);
}
schedule_work(&key_gc_work);
}
+ key_user_put(user);
}
}
EXPORT_SYMBOL(key_put);
next reply other threads:[~2025-03-18 10:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-18 10:14 David Howells [this message]
2025-03-18 11:22 ` [PATCH] keys: Fix UAF in key_put() Oleg Nesterov
2025-03-18 11:36 ` Oleg Nesterov
2025-03-18 13:27 ` David Howells
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