| Message ID | 1363180069-3733-1-git-send-email-luis.henriques@canonical.com |
|---|---|
| State | New |
| Headers | show |
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c index bb6f6ef..6f601ab 100644 --- a/security/keys/process_keys.c +++ b/security/keys/process_keys.c @@ -54,7 +54,7 @@ int install_user_keyrings(void) kenter("%p{%u}", user, user->uid); - if (user->uid_keyring) { + if (user->uid_keyring && user->session_keyring) { kleave(" = 0 [exist]"); return 0; }
This is a note to let you know that I have just added a patch titled keys: fix race with concurrent install_user_keyrings() to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From d2f0d64d3bbc0c92ead34c4f2e72ba7af9f6b309 Mon Sep 17 00:00:00 2001 From: David Howells <dhowells@redhat.com> Date: Tue, 12 Mar 2013 16:44:31 +1100 Subject: [PATCH] keys: fix race with concurrent install_user_keyrings() commit 0da9dfdd2cd9889201bc6f6f43580c99165cd087 upstream. This fixes CVE-2013-1792. There is a race in install_user_keyrings() that can cause a NULL pointer dereference when called concurrently for the same user if the uid and uid-session keyrings are not yet created. It might be possible for an unprivileged user to trigger this by calling keyctl() from userspace in parallel immediately after logging in. Assume that we have two threads both executing lookup_user_key(), both looking for KEY_SPEC_USER_SESSION_KEYRING. THREAD A THREAD B =============================== =============================== ==>call install_user_keyrings(); if (!cred->user->session_keyring) ==>call install_user_keyrings() ... user->uid_keyring = uid_keyring; if (user->uid_keyring) return 0; <== key = cred->user->session_keyring [== NULL] user->session_keyring = session_keyring; atomic_inc(&key->usage); [oops] At the point thread A dereferences cred->user->session_keyring, thread B hasn't updated user->session_keyring yet, but thread A assumes it is populated because install_user_keyrings() returned ok. The race window is really small but can be exploited if, for example, thread B is interrupted or preempted after initializing uid_keyring, but before doing setting session_keyring. This couldn't be reproduced on a stock kernel. However, after placing systemtap probe on 'user->session_keyring = session_keyring;' that introduced some delay, the kernel could be crashed reliably. Fix this by checking both pointers before deciding whether to return. Alternatively, the test could be done away with entirely as it is checked inside the mutex - but since the mutex is global, that may not be the best way. Signed-off-by: David Howells <dhowells@redhat.com> Reported-by: Mateusz Guzik <mguzik@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: James Morris <james.l.morris@oracle.com> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- security/keys/process_keys.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 1.8.1.2