On Fri, 18 Dec 2015, Linus Torvalds wrote:

> So there is no way in hell I am pulling this.

Sorry for the confusion.

Please pull the first patch from here:

The following changes since commit 73796d8bf27372e26c2b79881947304c14c2d353:

  Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net (2015-12-17 
14:05:22 -0800)

are available in the git repository at:


David Howells (1):
      KEYS: Fix race between read and revoke


 security/keys/keyctl.c |   18 +++++++++---------
 1 files changed, 9 insertions(+), 9 deletions(-)
commit b4a1b4f5047e4f54e194681125c74c0aa64d637d
Author: David Howells <dhowe...@redhat.com>
Date:   Fri Dec 18 01:34:26 2015 +0000

    KEYS: Fix race between read and revoke
    This fixes CVE-2015-7550.
    There's a race between keyctl_read() and keyctl_revoke().  If the revoke
    happens between keyctl_read() checking the validity of a key and the key's
    semaphore being taken, then the key type read method will see a revoked key.
    This causes a problem for the user-defined key type because it assumes in
    its read method that there will always be a payload in a non-revoked key
    and doesn't check for a NULL pointer.
    Fix this by making keyctl_read() check the validity of a key after taking
    semaphore instead of before.
    I think the bug was introduced with the original keyrings code.
    This was discovered by a multithreaded test program generated by syzkaller
    (http://github.com/google/syzkaller).  Here's a cleaned up version:
        #include <sys/types.h>
        #include <keyutils.h>
        #include <pthread.h>
        void *thr0(void *arg)
                key_serial_t key = (unsigned long)arg;
                return 0;
        void *thr1(void *arg)
                key_serial_t key = (unsigned long)arg;
                char buffer[16];
                keyctl_read(key, buffer, 16);
                return 0;
        int main()
                key_serial_t key = add_key("user", "%", "foo", 3, 
                pthread_t th[5];
                pthread_create(&th[0], 0, thr0, (void *)(unsigned long)key);
                pthread_create(&th[1], 0, thr1, (void *)(unsigned long)key);
                pthread_create(&th[2], 0, thr0, (void *)(unsigned long)key);
                pthread_create(&th[3], 0, thr1, (void *)(unsigned long)key);
                pthread_join(th[0], 0);
                pthread_join(th[1], 0);
                pthread_join(th[2], 0);
                pthread_join(th[3], 0);
                return 0;
    Build as:
        cc -o keyctl-race keyctl-race.c -lkeyutils -lpthread
    Run as:
        while keyctl-race; do :; done
    as it may need several iterations to crash the kernel.  The crash can be
    summarised as:
        BUG: unable to handle kernel NULL pointer dereference at 
        IP: [<ffffffff81279b08>] user_read+0x56/0xa3
        Call Trace:
         [<ffffffff81276aa9>] keyctl_read_key+0xb6/0xd7
         [<ffffffff81277815>] SyS_keyctl+0x83/0xe0
         [<ffffffff815dbb97>] entry_SYSCALL_64_fastpath+0x12/0x6f
    Reported-by: Dmitry Vyukov <dvyu...@google.com>
    Signed-off-by: David Howells <dhowe...@redhat.com>
    Tested-by: Dmitry Vyukov <dvyu...@google.com>
    Cc: sta...@vger.kernel.org
    Signed-off-by: James Morris <james.l.mor...@oracle.com>

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index fb111ea..1c3872a 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -751,16 +751,16 @@ long keyctl_read_key(key_serial_t keyid, char __user 
*buffer, size_t buflen)
        /* the key is probably readable - now try to read it */
-       ret = key_validate(key);
-       if (ret == 0) {
-               ret = -EOPNOTSUPP;
-               if (key->type->read) {
-                       /* read the data with the semaphore held (since we
-                        * might sleep) */
-                       down_read(&key->sem);
+       ret = -EOPNOTSUPP;
+       if (key->type->read) {
+               /* Read the data with the semaphore held (since we might sleep)
+                * to protect against the key being updated or revoked.
+                */
+               down_read(&key->sem);
+               ret = key_validate(key);
+               if (ret == 0)
                        ret = key->type->read(key, buffer, buflen);
-                       up_read(&key->sem);
-               }
+               up_read(&key->sem);
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