[PATCH] FS-Cache: fix dereference of NULL user_key_payload

[PATCH] FS-Cache: fix dereference of NULL user_key_payload

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

commit d124b2c53c7bee6569d2a2d0b18b4a1afde00134 upstream.  Please apply
to stable for 4.4 through 4.10.

When the file /proc/fs/fscache/objects (available with
CONFIG_FSCACHE_OBJECT_LIST=y) is opened, we request a user key with
description "fscache:objlist", then access its payload.  However, a
revoked key has a NULL payload, and we failed to check for this.
request_key() *does* skip revoked keys, but there is still a window
where the key can be revoked before we access its payload.

Fix it by checking for a NULL payload, treating it like a key which was
already revoked at the time it was requested.

Fixes: 4fbf4291aa15 ("FS-Cache: Allow the current state of all objects to be dumped")
Reviewed-by: James Morris <james.l.morris@oracle.com>
Cc: <stable@vger.kernel.org>    [v2.6.32+]
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---
 fs/fscache/object-list.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
index 5d5ddaa84b21..37e0c31d284f 100644
--- a/fs/fscache/object-list.c
+++ b/fs/fscache/object-list.c
@@ -330,6 +330,13 @@ static void fscache_objlist_config(struct fscache_objlist_data *data)
 	rcu_read_lock();
 
 	confkey = user_key_payload(key);
+	if (!confkey) {
+		/* key was revoked */
+		rcu_read_unlock();
+		key_put(key);
+		goto no_config;
+	}
+
 	buf = confkey->data;
 
 	for (len = confkey->datalen - 1; len >= 0; len--) {
-- 
2.15.0.rc0.271.g36b669edcc-goog

Re: [PATCH] FS-Cache: fix dereference of NULL user_key_payload

[Greg KH]

On Tue, Oct 24, 2017 at 04:43:20PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> commit d124b2c53c7bee6569d2a2d0b18b4a1afde00134 upstream.  Please apply
> to stable for 4.4 through 4.10.

Thanks for this, now queued up.

greg k-h

[PATCH] FS-Cache: fix dereference of NULL user_key_payload

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

commit d124b2c53c7bee6569d2a2d0b18b4a1afde00134 upstream.  Please apply
to stable for 4.3 and earlier.

When the file /proc/fs/fscache/objects (available with
CONFIG_FSCACHE_OBJECT_LIST=y) is opened, we request a user key with
description "fscache:objlist", then access its payload.  However, a
revoked key has a NULL payload, and we failed to check for this.
request_key() *does* skip revoked keys, but there is still a window
where the key can be revoked before we access its payload.

Fix it by checking for a NULL payload, treating it like a key which was
already revoked at the time it was requested.

Fixes: 4fbf4291aa15 ("FS-Cache: Allow the current state of all objects to be dumped")
Reviewed-by: James Morris <james.l.morris@oracle.com>
Cc: <stable@vger.kernel.org>    [v2.6.32+]
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---
 fs/fscache/object-list.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
index 51dde817e1f2..11cf71ac1cb5 100644
--- a/fs/fscache/object-list.c
+++ b/fs/fscache/object-list.c
@@ -330,6 +330,13 @@ static void fscache_objlist_config(struct fscache_objlist_data *data)
 	rcu_read_lock();
 
 	confkey = key->payload.data;
+	if (!confkey) {
+		/* key was revoked */
+		rcu_read_unlock();
+		key_put(key);
+		goto no_config;
+	}
+
 	buf = confkey->data;
 
 	for (len = confkey->datalen - 1; len >= 0; len--) {
-- 
2.15.0.rc0.271.g36b669edcc-goog

Re: [PATCH] FS-Cache: fix dereference of NULL user_key_payload

[Greg KH]

On Tue, Oct 24, 2017 at 04:44:47PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> commit d124b2c53c7bee6569d2a2d0b18b4a1afde00134 upstream.  Please apply
> to stable for 4.3 and earlier.

Applied to 3.18, thanks.

greg k-h