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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
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