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Message-ID: <20250318112245.GA14792@redhat.com>
Date: Tue, 18 Mar 2025 12:22:46 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: David Howells <dhowells@...hat.com>
Cc: Jarkko Sakkinen <jarkko@...nel.org>, Kees Cook <kees@...nel.org>,
Greg KH <gregkh@...uxfoundation.org>,
Josh Drake <josh@...phoslabs.com>,
Suraj Sonawane <surajsonawane0215@...il.com>,
keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
security@...nel.org, stable@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] keys: Fix UAF in key_put()
On 03/18, David Howells wrote:
>
> --- 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);
Do we really need the unconditional refcount_inc / key_user_put ?
void key_put(struct key *key)
{
if (key) {
struct key_user *user = NULL;
unsigned short len;
key_check(key);
if (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 (user) {
spin_lock_irqsave(&user->lock, flags);
user->qnkeys--;
user->qnbytes -= len;
spin_unlock_irqrestore(&user->lock, flags);
}
schedule_work(&key_gc_work);
}
if (user)
key_user_put(user);
}
}
looks a bit more clear/simple to me...
Oleg.
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