From f05819df10d7b09f6d1eb6f8534a8f68e5a4fe61 Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 15 Oct 2015 17:21:37 +0100 Subject: [PATCH 1/2] KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring 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: [] keyring_destroy+0x3d/0x88 ... Workqueue: events key_garbage_collector ... RIP: 0010:[] 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: [] key_gc_unused_keys.constprop.1+0x5d/0x10f [] key_garbage_collector+0x1fa/0x351 [] process_one_work+0x28e/0x547 [] worker_thread+0x26e/0x361 [] ? rescuer_thread+0x2a8/0x2a8 [] kthread+0xf3/0xfb [] ? kthread_create_on_node+0x1c2/0x1c2 [] ret_from_fork+0x3f/0x70 [] ? 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 Signed-off-by: David Howells Tested-by: Dmitry Vyukov --- 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 39eac1fd5706..addf060399e0 100644 --- a/security/keys/gc.c +++ b/security/keys/gc.c @@ -134,8 +134,10 @@ 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); From 911b79cde95c7da0ec02f48105358a36636b7a71 Mon Sep 17 00:00:00 2001 From: David Howells Date: Mon, 19 Oct 2015 11:20:28 +0100 Subject: [PATCH 2/2] KEYS: Don't permit request_key() to construct a new keyring If request_key() is used to find a keyring, only do the search part - don't do the construction part if the keyring was not found by the search. We don't really want keyrings in the negative instantiated state since the rejected/negative instantiation error value in the payload is unioned with keyring metadata. Now the kernel gives an error: request_key("keyring", "#selinux,bdekeyring", "keyring", KEY_SPEC_USER_SESSION_KEYRING) = -1 EPERM (Operation not permitted) Signed-off-by: David Howells --- security/keys/request_key.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/security/keys/request_key.c b/security/keys/request_key.c index 486ef6fa393b..0d6253124278 100644 --- a/security/keys/request_key.c +++ b/security/keys/request_key.c @@ -440,6 +440,9 @@ static struct key *construct_key_and_link(struct keyring_search_context *ctx, kenter(""); + if (ctx->index_key.type == &key_type_keyring) + return ERR_PTR(-EPERM); + user = key_user_lookup(current_fsuid()); if (!user) return ERR_PTR(-ENOMEM);