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SubjectRe: [PATCH] KEYS: Make the keyring cycle detector ignore other keyrings of the same name
Acked-by: James Morris <james.l.morris@oracle.com>


On Tue, 4 Mar 2014, David Howells wrote:

>
> This fixes CVE-2014-0102.
>
> The following command sequence produces an oops:
>
> keyctl new_session
> i=`keyctl newring _ses @s`
> keyctl link @s $i
>
> The problem is that search_nested_keyrings() sees two keyrings that have
> matching type and description, so keyring_compare_object() returns true.
> s_n_k() then passes the key to the iterator function -
> keyring_detect_cycle_iterator() - which *should* check to see whether this is
> the keyring of interest, not just one with the same name.
>
> Because assoc_array_find() will return one and only one match, I assumed that
> the iterator function would only see an exact match or never be called - but
> the iterator isn't only called from assoc_array_find()...
>
> The oops looks something like this:
>
> kernel BUG at /data/fs/linux-2.6-fscache/security/keys/keyring.c:1003!
> invalid opcode: 0000 [#1] SMP
> ...
> RIP: 0010:[<ffffffff811d39c3>] keyring_detect_cycle_iterator+0xe/0x1f
> ...
> Stack:
> ...
> Call Trace:
> [<ffffffff811d3706>] search_nested_keyrings+0x76/0x2aa
> [<ffffffff810fa7f4>] ? kmem_cache_alloc_trace+0xdd/0x159
> [<ffffffff81235669>] ? assoc_array_insert+0xab/0x929
> [<ffffffff811e226d>] ? selinux_key_permission+0x2d/0x2f
> [<ffffffff811dc94c>] ? security_key_permission+0x11/0x13
> [<ffffffff811d3e36>] __key_link_check_live_key+0x50/0x5f
> [<ffffffff811d39b5>] ? keyring_describe+0x7b/0x7b
> [<ffffffff811d3f2b>] key_link+0x4e/0x85
> [<ffffffff811d463a>] keyctl_keyring_link+0x60/0x81
> [<ffffffff811d553d>] SyS_keyctl+0x65/0xe4
> [<ffffffff81452edb>] tracesys+0xdd/0xe2
>
> The fix is to make keyring_detect_cycle_iterator() check that the key it has
> is the key it was actually looking for rather than calling BUG_ON().
>
> A testcase has been included in the keyutils testsuite for this:
>
> http://git.kernel.org/cgit/linux/kernel/git/dhowells/keyutils.git/commit/?id=891f3365d07f1996778ade0e3428f01878a1790b
>
> Reported-by: Tommi Rantala <tt.rantala@gmail.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
> diff --git a/security/keys/keyring.c b/security/keys/keyring.c
> index d46cbc5e335e..2fb2576dc644 100644
> --- a/security/keys/keyring.c
> +++ b/security/keys/keyring.c
> @@ -1000,7 +1000,11 @@ static int keyring_detect_cycle_iterator(const void *object,
>
> kenter("{%d}", key->serial);
>
> - BUG_ON(key != ctx->match_data);
> + /* We might get a keyring with matching index-key that is nonetheless a
> + * different keyring. */
> + if (key != ctx->match_data)
> + return 0;
> +
> ctx->result = ERR_PTR(-EDEADLK);
> return 1;
> }
> --
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>

--
James Morris
<jmorris@namei.org>


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