[request for stable 3.x 4.1 inclusion][PATCH 0/2] fix for security/keys

[request for stable 3.x 4.1 inclusion][PATCH 0/2] fix for security/keys

[Wang Kai]

The first patch is a bugfix for race condition.
The second patch is the fix for CVE-2015-7872.
Backport first one will make second CVE fix directly cherry-picked.

Stable 3.2.y has included these 2 patches in v3.2.73.

Stable 3.1x.y and 4.1.y can cherry-pick these 2 patches.

Stable 3.4.y can cherry-pick the backported patches in 3.2.y which
ID are below: 
a6826ecbeab9c832ed742653de895ad4de61c858
  KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring
650f6aa8c3c805bd41c4243aadbd63558f39fd32
  KEYS: Fix race between key destruction and finding a keyring by name

David Howells (2):
  KEYS: Fix race between key destruction and finding a keyring by name
  KEYS: Fix crash when attempt to garbage collect an uninstantiated
    keyring

 security/keys/gc.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

-- 
1.8.3.4

[PATCH 1/2] KEYS: Fix race between key destruction and finding a keyring by name

[Wang Kai]

From: David Howells <dhowells@redhat.com>

commit 94c4554ba07adbdde396748ee7ae01e86cf2d8d7 upstream.

There appears to be a race between:

 (1) key_gc_unused_keys() which frees key->security and then calls
     keyring_destroy() to unlink the name from the name list

 (2) find_keyring_by_name() which calls key_permission(), thus accessing
     key->security, on a key before checking to see whether the key usage is 0
     (ie. the key is dead and might be cleaned up).

Fix this by calling ->destroy() before cleaning up the core key data -
including key->security.

Reported-by: Petr Matousek <pmatouse@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---
 security/keys/gc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index 7978186..483ebdf 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -187,6 +187,10 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
 		kdebug("- %u", key->serial);
 		key_check(key);
 
+		/* Throw away the key data */
+		if (key->type->destroy)
+			key->type->destroy(key);
+
 		security_key_free(key);
 
 		/* deal with the user's key tracking and quota */
@@ -201,10 +205,6 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
 		if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 			atomic_dec(&key->user->nikeys);
 
-		/* now throw away the key memory */
-		if (key->type->destroy)
-			key->type->destroy(key);
-
 		key_user_put(key->user);
 
 		kfree(key->description);
-- 
1.8.3.4

[PATCH 2/2] KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring

[Wang Kai]

From: David Howells <dhowells@redhat.com>

commit f05819df10d7b09f6d1eb6f8534a8f68e5a4fe61 upstream.

The following sequence of commands:

    i=`keyctl add user a a @s`
    keyctl request2 keyring foo bar @t
    keyctl unlink $i @s

tries to invoke an upcall to instantiate a keyring if one doesn't already
exist by that name within the user's keyring set.  However, if the upcall
fails, the code sets keyring->type_data.reject_error to -ENOKEY or some
other error code.  When the key is garbage collected, the key destroy
function is called unconditionally and keyring_destroy() uses list_empty()
on keyring->type_data.link - which is in a union with reject_error.
Subsequently, the kernel tries to unlink the keyring from the keyring names
list - which oopses like this:

	BUG: unable to handle kernel paging request at 00000000ffffff8a
	IP: [<ffffffff8126e051>] keyring_destroy+0x3d/0x88
	...
	Workqueue: events key_garbage_collector
	...
	RIP: 0010:[<ffffffff8126e051>] keyring_destroy+0x3d/0x88
	RSP: 0018:ffff88003e2f3d30  EFLAGS: 00010203
	RAX: 00000000ffffff82 RBX: ffff88003bf1a900 RCX: 0000000000000000
	RDX: 0000000000000000 RSI: 000000003bfc6901 RDI: ffffffff81a73a40
	RBP: ffff88003e2f3d38 R08: 0000000000000152 R09: 0000000000000000
	R10: ffff88003e2f3c18 R11: 000000000000865b R12: ffff88003bf1a900
	R13: 0000000000000000 R14: ffff88003bf1a908 R15: ffff88003e2f4000
	...
	CR2: 00000000ffffff8a CR3: 000000003e3ec000 CR4: 00000000000006f0
	...
	Call Trace:
	 [<ffffffff8126c756>] key_gc_unused_keys.constprop.1+0x5d/0x10f
	 [<ffffffff8126ca71>] key_garbage_collector+0x1fa/0x351
	 [<ffffffff8105ec9b>] process_one_work+0x28e/0x547
	 [<ffffffff8105fd17>] worker_thread+0x26e/0x361
	 [<ffffffff8105faa9>] ? rescuer_thread+0x2a8/0x2a8
	 [<ffffffff810648ad>] kthread+0xf3/0xfb
	 [<ffffffff810647ba>] ? kthread_create_on_node+0x1c2/0x1c2
	 [<ffffffff815f2ccf>] ret_from_fork+0x3f/0x70
	 [<ffffffff810647ba>] ? kthread_create_on_node+0x1c2/0x1c2

Note the value in RAX.  This is a 32-bit representation of -ENOKEY.

The solution is to only call ->destroy() if the key was successfully
instantiated.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
---
 security/keys/gc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index 483ebdf..de34c29 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -187,8 +187,10 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
 		kdebug("- %u", key->serial);
 		key_check(key);
 
-		/* Throw away the key data */
-		if (key->type->destroy)
+		/* Throw away the key data if the key is instantiated */
+		if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags) &&
+		    !test_bit(KEY_FLAG_NEGATIVE, &key->flags) &&
+		    key->type->destroy)
 			key->type->destroy(key);
 
 		security_key_free(key);
-- 
1.8.3.4

Re: [request for stable 3.x 4.1 inclusion][PATCH 0/2] fix for security/keys

[Jiri Slaby]

On 11/18/2015, 09:14 AM, Wang Kai wrote:
> The first patch is a bugfix for race condition.
> The second patch is the fix for CVE-2015-7872.
> Backport first one will make second CVE fix directly cherry-picked.
> 
> Stable 3.2.y has included these 2 patches in v3.2.73.
> 
> Stable 3.1x.y and 4.1.y can cherry-pick these 2 patches.

Done for 3.12. Thanks!

-- 
js
suse labs

Re: [request for stable 3.x 4.1 inclusion][PATCH 0/2] fix for security/keys

[Greg KH]

On Wed, Nov 18, 2015 at 08:14:48AM +0000, Wang Kai wrote:
> The first patch is a bugfix for race condition.
> The second patch is the fix for CVE-2015-7872.
> Backport first one will make second CVE fix directly cherry-picked.
> 
> Stable 3.2.y has included these 2 patches in v3.2.73.
> 
> Stable 3.1x.y and 4.1.y can cherry-pick these 2 patches.

Now applied, thanks.

greg k-h