If a user key gets negatively instantiated, an error code is cached in the
payload area. A negatively instantiated key may be then be positively
instantiated by updating it with valid data. However, the ->update key
type method must be aware that the error code may be there.
The following may be used to trigger the bug in the user key type:
keyctl request2 user user "" @u
keyctl add user user "a" @u
which manifests itself as:
BUG: unable to handle kernel paging request at 00000000ffffff8a
IP: [<ffffffff810a376f>] __call_rcu.constprop.76+0x1f/0x280 kernel/rcu/tree.c:3046
PGD 7cc30067 PUD 0
Oops: 0002 [#1] SMP
Modules linked in:
CPU: 3 PID: 2644 Comm: a.out Not tainted 4.3.0+ #49
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88003ddea700 ti: ffff88003dd88000 task.ti: ffff88003dd88000
RIP: 0010:[<ffffffff810a376f>] [<ffffffff810a376f>] __call_rcu.constprop.76+0x1f/0x280
[<ffffffff810a376f>] __call_rcu.constprop.76+0x1f/0x280 kernel/rcu/tree.c:3046
RSP: 0018:ffff88003dd8bdb0 EFLAGS: 00010246
RAX: 00000000ffffff82 RBX: 0000000000000000 RCX: 0000000000000001
RDX: ffffffff81e3fe40 RSI: 0000000000000000 RDI: 00000000ffffff82
RBP: ffff88003dd8bde0 R08: ffff88007d2d2da0 R09: 0000000000000000
R10: 0000000000000000 R11: ffff88003e8073c0 R12: 00000000ffffff82
R13: ffff88003dd8be68 R14: ffff88007d027600 R15: ffff88003ddea700
FS: 0000000000b92880(0063) GS:ffff88007fd00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00000000ffffff8a CR3: 000000007cc5f000 CR4: 00000000000006e0
Stack:
ffff88003dd8bdf0 ffffffff81160a8a 0000000000000000 00000000ffffff82
ffff88003dd8be68 ffff88007d027600 ffff88003dd8bdf0 ffffffff810a39e5
ffff88003dd8be20 ffffffff812a31ab ffff88007d027600 ffff88007d027620
Call Trace:
[<ffffffff810a39e5>] kfree_call_rcu+0x15/0x20 kernel/rcu/tree.c:3136
[<ffffffff812a31ab>] user_update+0x8b/0xb0 security/keys/user_defined.c:129
[< inline >] __key_update security/keys/key.c:730
[<ffffffff8129e5c1>] key_create_or_update+0x291/0x440 security/keys/key.c:908
[< inline >] SYSC_add_key security/keys/keyctl.c:125
[<ffffffff8129fc21>] SyS_add_key+0x101/0x1e0 security/keys/keyctl.c:60
[<ffffffff8185f617>] entry_SYSCALL_64_fastpath+0x12/0x6a arch/x86/entry/entry_64.S:185
Note the error code (-ENOKEY) in EDX.
A similar bug can be tripped by:
keyctl request2 trusted user "" @u
keyctl add trusted user "a" @u
This should also affect encrypted keys - but that has to be correctly
parameterised or it will fail with EINVAL before getting to the bit that
will crashes.
Reported-by: Dmitry Vyukov <[email protected]>
Signed-off-by: David Howells <[email protected]>
Acked-by: Mimi Zohar <[email protected]>
---
security/keys/encrypted-keys/encrypted.c | 2 ++
security/keys/trusted.c | 5 ++++-
security/keys/user_defined.c | 5 ++++-
3 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
index 927db9f35ad6..696ccfa08d10 100644
--- a/security/keys/encrypted-keys/encrypted.c
+++ b/security/keys/encrypted-keys/encrypted.c
@@ -845,6 +845,8 @@ static int encrypted_update(struct key *key, struct key_preparsed_payload *prep)
size_t datalen = prep->datalen;
int ret = 0;
+ if (test_bit(KEY_FLAG_NEGATIVE, &key->flags))
+ return -ENOKEY;
if (datalen <= 0 || datalen > 32767 || !prep->data)
return -EINVAL;
diff --git a/security/keys/trusted.c b/security/keys/trusted.c
index 903dace648a1..16dec53184b6 100644
--- a/security/keys/trusted.c
+++ b/security/keys/trusted.c
@@ -1007,13 +1007,16 @@ static void trusted_rcu_free(struct rcu_head *rcu)
*/
static int trusted_update(struct key *key, struct key_preparsed_payload *prep)
{
- struct trusted_key_payload *p = key->payload.data[0];
+ struct trusted_key_payload *p;
struct trusted_key_payload *new_p;
struct trusted_key_options *new_o;
size_t datalen = prep->datalen;
char *datablob;
int ret = 0;
+ if (test_bit(KEY_FLAG_NEGATIVE, &key->flags))
+ return -ENOKEY;
+ p = key->payload.data[0];
if (!p->migratable)
return -EPERM;
if (datalen <= 0 || datalen > 32767 || !prep->data)
diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c
index 28cb30f80256..8705d79b2c6f 100644
--- a/security/keys/user_defined.c
+++ b/security/keys/user_defined.c
@@ -120,7 +120,10 @@ int user_update(struct key *key, struct key_preparsed_payload *prep)
if (ret == 0) {
/* attach the new data, displacing the old */
- zap = key->payload.data[0];
+ if (!test_bit(KEY_FLAG_NEGATIVE, &key->flags))
+ zap = key->payload.data[0];
+ else
+ zap = NULL;
rcu_assign_keypointer(key, upayload);
key->expiry = 0;
}
Hi James,
Can this be passed straight to Linus please?
Thanks,
David
On Tue, 24 Nov 2015, David Howells wrote:
> Hi James,
>
> Can this be passed straight to Linus please?
Is this triggerable by normal users?
--
James Morris
<[email protected]>
James Morris <[email protected]> wrote:
> Is this triggerable by normal users?
Yes.
David