Fix incorrect updates of uninstantiated keys crash the kernel (rhbz 1498017)

1 files changed, 130 insertions, 0 deletions

diff --git a/KEYS-don-t-let-add_key-update-an-uninstantiated-key.patch b/KEYS-don-t-let-add_key-update-an-uninstantiated-key.patch
new file mode 100644
index 000000000..af7478ee5
--- /dev/null
+++ b/KEYS-don-t-let-add_key-update-an-uninstantiated-key.patch
@@ -0,0 +1,130 @@
+From 7289bfaee2a42bdb56eecab0625907c045d080ba Mon Sep 17 00:00:00 2001
+From: Eric Biggers <ebiggers@google.com>
+Date: Wed, 27 Sep 2017 12:50:41 -0700
+Subject: [PATCH] KEYS: don't let add_key() update an uninstantiated key
+
+Currently, add_key() will, when passed a key that already exists, call
+the key's ->update() method.  But this is heavily broken in the case
+where the key is uninstantiated because it doesn't call
+__key_instantiate_and_link().  Consequently, it doesn't do most of the
+things that are supposed to happen when the key is instantiated, such as
+setting KEY_FLAG_INSTANTIATED, clearing KEY_FLAG_USER_CONSTRUCT and
+awakening tasks waiting on it, and incrementing key->user->nikeys.
+
+It also never takes key_construction_mutex, which means that
+->instantiate() can run concurrently with ->update() on the same key.
+In the case of the "user" and "logon" key types this causes a memory
+leak, at best.  Maybe even worse, the ->update() methods of the
+"encrypted" and "trusted" key types actually just dereference a NULL
+pointer when passed an uninstantiated key.
+
+Therefore, change find_key_to_update() to return NULL if the found key
+is uninstantiated, so that add_key() replaces the key rather than
+instantiating it.  This seems to be better than fixing __key_update() to
+call __key_instantiate_and_link(), since given all the bugs noted above
+as well as that the existing behavior was undocumented and
+keyctl_instantiate() is supposed to be used instead, I doubt anyone was
+relying on the existing behavior.
+
+This patch only affects *uninstantiated* keys.  For now we still allow a
+negatively instantiated key to be updated (thereby positively
+instantiating it), although that's broken too (the next patch fixes it)
+and I'm not sure that anyone actually uses that functionality either.
+
+Here is a simple reproducer for the bug using the "encrypted" key type
+(requires CONFIG_ENCRYPTED_KEYS=y), though as noted above the bug
+pertained to more than just the "encrypted" key type:
+
+    #include <stdlib.h>
+    #include <unistd.h>
+    #include <keyutils.h>
+
+    int main(void)
+    {
+        int ringid = keyctl_join_session_keyring(NULL);
+
+        if (fork()) {
+            for (;;) {
+                const char payload[] = "update user:foo 32";
+
+                usleep(rand() % 10000);
+                add_key("encrypted", "desc", payload, sizeof(payload), ringid);
+                keyctl_clear(ringid);
+            }
+        } else {
+            for (;;)
+                request_key("encrypted", "desc", "callout_info", ringid);
+        }
+    }
+
+It causes:
+
+    BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
+    IP: encrypted_update+0xb0/0x170
+    PGD 7a178067 P4D 7a178067 PUD 77269067 PMD 0
+    PREEMPT SMP
+    CPU: 0 PID: 340 Comm: reproduce Tainted: G      D         4.14.0-rc1-00025-g428490e38b2e #796
+    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
+    task: ffff8a467a39a340 task.stack: ffffb15c40770000
+    RIP: 0010:encrypted_update+0xb0/0x170
+    RSP: 0018:ffffb15c40773de8 EFLAGS: 00010246
+    RAX: 0000000000000000 RBX: ffff8a467a275b00 RCX: 0000000000000000
+    RDX: 0000000000000005 RSI: ffff8a467a275b14 RDI: ffffffffb742f303
+    RBP: ffffb15c40773e20 R08: 0000000000000000 R09: ffff8a467a275b17
+    R10: 0000000000000020 R11: 0000000000000000 R12: 0000000000000000
+    R13: 0000000000000000 R14: ffff8a4677057180 R15: ffff8a467a275b0f
+    FS:  00007f5d7fb08700(0000) GS:ffff8a467f200000(0000) knlGS:0000000000000000
+    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
+    CR2: 0000000000000018 CR3: 0000000077262005 CR4: 00000000001606f0
+    Call Trace:
+     key_create_or_update+0x2bc/0x460
+     SyS_add_key+0x10c/0x1d0
+     entry_SYSCALL_64_fastpath+0x1f/0xbe
+    RIP: 0033:0x7f5d7f211259
+    RSP: 002b:00007ffed03904c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000f8
+    RAX: ffffffffffffffda RBX: 000000003b2a7955 RCX: 00007f5d7f211259
+    RDX: 00000000004009e4 RSI: 00000000004009ff RDI: 0000000000400a04
+    RBP: 0000000068db8bad R08: 000000003b2a7955 R09: 0000000000000004
+    R10: 000000000000001a R11: 0000000000000246 R12: 0000000000400868
+    R13: 00007ffed03905d0 R14: 0000000000000000 R15: 0000000000000000
+    Code: 77 28 e8 64 34 1f 00 45 31 c0 31 c9 48 8d 55 c8 48 89 df 48 8d 75 d0 e8 ff f9 ff ff 85 c0 41 89 c4 0f 88 84 00 00 00 4c 8b 7d c8 <49> 8b 75 18 4c 89 ff e8 24 f8 ff ff 85 c0 41 89 c4 78 6d 49 8b
+    RIP: encrypted_update+0xb0/0x170 RSP: ffffb15c40773de8
+    CR2: 0000000000000018
+
+Cc: <stable@vger.kernel.org>    [v2.6.12+]
+Signed-off-by: Eric Biggers <ebiggers@google.com>
+---
+ security/keys/keyring.c | 10 ++++++----
+ 1 file changed, 6 insertions(+), 4 deletions(-)
+
+diff --git a/security/keys/keyring.c b/security/keys/keyring.c
+index 4fa82a8a9c0e..129a4175760b 100644
+--- a/security/keys/keyring.c
++++ b/security/keys/keyring.c
+@@ -1056,8 +1056,8 @@ EXPORT_SYMBOL(keyring_restrict);
+  * caller must also hold a lock on the keyring semaphore.
+  *
+  * Returns a pointer to the found key with usage count incremented if
+- * successful and returns NULL if not found.  Revoked and invalidated keys are
+- * skipped over.
++ * successful and returns NULL if not found.  Revoked, invalidated, and
++ * uninstantiated keys are skipped over.  (But negative keys are not!)
+  *
+  * If successful, the possession indicator is propagated from the keyring ref
+  * to the returned key reference.
+@@ -1084,8 +1084,10 @@ key_ref_t find_key_to_update(key_ref_t keyring_ref,
+ 
+ found:
+ 	key = keyring_ptr_to_key(object);
+-	if (key->flags & ((1 << KEY_FLAG_INVALIDATED) |
+-			  (1 << KEY_FLAG_REVOKED))) {
++	if ((key->flags & ((1 << KEY_FLAG_INVALIDATED) |
++			   (1 << KEY_FLAG_REVOKED) |
++			   (1 << KEY_FLAG_INSTANTIATED))) !=
++	    (1 << KEY_FLAG_INSTANTIATED)) {
+ 		kleave(" = NULL [x]");
+ 		return NULL;
+ 	}
+-- 
+2.13.6
+