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