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authorJosh Boyer <jwboyer@fedoraproject.org>2015-12-14 10:40:27 -0500
committerJosh Boyer <jwboyer@fedoraproject.org>2015-12-14 10:40:27 -0500
commit47e44286b05205e9cdd3e5db1043616e1b05074b (patch)
treececefd7f61fa7d35e99433517f7c0dbfc4460bb3
parent129e0739fd0d3a50c31186ae89b3dc204a3ef31a (diff)
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CVE-2015-7550 Race between read and revoke keys (rhbz 1291197 1291198)
-rw-r--r--KEYS-Fix-race-between-read-and-revoke.patch108
-rw-r--r--kernel.spec6
2 files changed, 114 insertions, 0 deletions
diff --git a/KEYS-Fix-race-between-read-and-revoke.patch b/KEYS-Fix-race-between-read-and-revoke.patch
new file mode 100644
index 000000000..df0d9376b
--- /dev/null
+++ b/KEYS-Fix-race-between-read-and-revoke.patch
@@ -0,0 +1,108 @@
+From f144220f72062ed5359e0211f130670c915a12dd Mon Sep 17 00:00:00 2001
+From: David Howells <dhowells@redhat.com>
+Date: Mon, 14 Dec 2015 10:36:31 -0500
+Subject: [PATCH] KEYS: Fix race between read and revoke
+
+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.
+
+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;
+ keyctl_revoke(key);
+ 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, KEY_SPEC_USER_KEYRING);
+ 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 0000000000000010
+ 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 <dvyukov@google.com>
+Signed-off-by: David Howells <dhowells@redhat.com>
+---
+ security/keys/keyctl.c | 18 +++++++++---------
+ 1 file changed, 9 insertions(+), 9 deletions(-)
+
+diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
+index fb111eafcb89..1c3872aeed14 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 */
+ can_read_key:
+- 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);
+ }
+
+ error2:
+--
+2.5.0
+
diff --git a/kernel.spec b/kernel.spec
index ad7711998..2eab78d22 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -597,6 +597,9 @@ Patch571: ideapad-laptop-Add-Lenovo-ideapad-Y700-17ISK-to-no_h.patch
#rhbz 1288687
Patch572: alua_fix.patch
+#CVE-2015-7550 rhbz 1291197 1291198
+Patch575: KEYS-Fix-race-between-read-and-revoke.patch
+
# END OF PATCH DEFINITIONS
%endif
@@ -2040,6 +2043,9 @@ fi
#
#
%changelog
+* Mon Dec 14 2015 Josh Boyer <jwboyer@fedoraproject.org>
+- CVE-2015-7550 Race between read and revoke keys (rhbz 1291197 1291198)
+
* Fri Dec 11 2015 Laura Abbott <labbott@redhat.com> - 4.4.0-0.rc4.git4.1
- Linux v4.4-rc4-113-g0bd0f1e