From 10bde99768d3c92f5fde1ec51f74e926fc4cf779 Mon Sep 17 00:00:00 2001
From: Artem Savkov <asavkov@redhat.com>
Date: Thu, 27 Jan 2022 11:44:06 +0100
Subject: [KPATCH CVE-2021-0920] af_unix: fix garbage collect vs MSG_PEEK
Kernels:
- 3.10.0-1160.15.2.el7
- 3.10.0-1160.21.1.el7
- 3.10.0-1160.24.1.el7
- 3.10.0-1160.25.1.el7
- 3.10.0-1160.31.1.el7
- 3.10.0-1160.36.2.el7
- 3.10.0-1160.41.1.el7
- 3.10.0-1160.42.2.el7
- 3.10.0-1160.45.1.el7
- 3.10.0-1160.49.1.el7
- 3.10.0-1160.53.1.el7
Changes since last build:
arches: x86_64 ppc64le
- af_unix.o: changed function: unix_dgram_recvmsg
- af_unix.o: changed function: unix_stream_read_generic
- garbage.o: new function: unix_peek_fds
----
Kpatch-MR: https://gitlab.com/redhat/prdsc/rhel/src/kpatch/rhel-7/-/merge_requests/18
Approved-by: Joe Lawrence (@joe.lawrence)
Approved-by: Yannick Cote (@ycote1)
Kernels:
3.10.0-1160.21.1.el7
3.10.0-1160.24.1.el7
3.10.0-1160.25.1.el7
3.10.0-1160.31.1.el7
3.10.0-1160.36.2.el7
3.10.0-1160.41.1.el7
3.10.0-1160.42.2.el7
3.10.0-1160.45.1.el7
3.10.0-1160.49.1.el7
3.10.0-1160.53.1.el7
Modifications: moved unix_peek_fds() to net/unix/garbage.c to avoid
changing unix_gc_lock scope.
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2031986
Z-MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-7/-/merge_requests/379
commit ab0fd1713f1efeb2c859d32721625ea98cd9e663
Author: William Zhao <wizhao@redhat.com>
Date: Wed Jan 19 09:29:17 2022 -0500
af_unix: fix garbage collect vs MSG_PEEK
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2031970
Upstream Status: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
CVE: CVE-2021-0920
Conflicts: The code still uses the old "sock_iocb" structure since rhel-7
does not have the commit 7cc05662682da ("net: remove sock_iocb"). Thus
passing the "scm_cookie" pointer to the "unix_peek_fds" was slightly
modified to use "siocb->scm" instead of just "&scm". Additionally
the "unix_gc_lock" is not exposed to "af_unix.c" via a header file since
rhel-7 does not have the commit f4e65870e5ce ("net: split out functions
related to registering inflight socket files"). Bringing in the commit
will add a new UNIX_SCM kernel config; this can be avoided by adding
extern-ing the "unix_gc_lock".
commit cbcf01128d0a92e131bd09f1688fe032480b65ca
Author: Miklos Szeredi <mszeredi@redhat.com>
Date: Wed Jul 28 14:47:20 2021 +0200
af_unix: fix garbage collect vs MSG_PEEK
unix_gc() assumes that candidate sockets can never gain an external
reference (i.e. be installed into an fd) while the unix_gc_lock is
held. Except for MSG_PEEK this is guaranteed by modifying inflight
count under the unix_gc_lock.
MSG_PEEK does not touch any variable protected by unix_gc_lock (file
count is not), yet it needs to be serialized with garbage collection.
Do this by locking/unlocking unix_gc_lock:
1) increment file count
2) lock/unlock barrier to make sure incremented file count is visible
to garbage collection
3) install file into fd
This is a lock barrier (unlike smp_mb()) that ensures that garbage
collection is run completely before or completely after the barrier.
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: William Zhao <wizhao@redhat.com>
Signed-off-by: Artem Savkov <asavkov@redhat.com>
---
net/unix/af_unix.c | 7 +++++--
net/unix/garbage.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 52 insertions(+), 2 deletions(-)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index bcb0ad54b9b3..a264b4598872 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1468,6 +1468,8 @@ out:
return err;
}
+void unix_peek_fds(struct scm_cookie *scm, struct sk_buff *skb);
+
static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
{
int i;
@@ -2182,7 +2184,8 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
sk_peek_offset_fwd(sk, size);
if (UNIXCB(skb).fp)
- siocb->scm->fp = scm_fp_dup(UNIXCB(skb).fp);
+ unix_peek_fds(siocb->scm, skb);
+
}
err = (flags & MSG_TRUNC) ? skb->len - skip : size;
@@ -2432,7 +2435,7 @@ unlock:
/* It is questionable, see note in unix_dgram_recvmsg.
*/
if (UNIXCB(skb).fp)
- siocb->scm->fp = scm_fp_dup(UNIXCB(skb).fp);
+ unix_peek_fds(siocb->scm, skb);
sk_peek_offset_fwd(sk, chunk);
diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index c36757e72844..f242268477ba 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -374,3 +374,50 @@ void unix_gc(void)
out:
spin_unlock(&unix_gc_lock);
}
+
+void unix_peek_fds(struct scm_cookie *scm, struct sk_buff *skb)
+{
+ scm->fp = scm_fp_dup(UNIXCB(skb).fp);
+
+ /*
+ * Garbage collection of unix sockets starts by selecting a set of
+ * candidate sockets which have reference only from being in flight
+ * (total_refs == inflight_refs). This condition is checked once during
+ * the candidate collection phase, and candidates are marked as such, so
+ * that non-candidates can later be ignored. While inflight_refs is
+ * protected by unix_gc_lock, total_refs (file count) is not, hence this
+ * is an instantaneous decision.
+ *
+ * Once a candidate, however, the socket must not be reinstalled into a
+ * file descriptor while the garbage collection is in progress.
+ *
+ * If the above conditions are met, then the directed graph of
+ * candidates (*) does not change while unix_gc_lock is held.
+ *
+ * Any operations that changes the file count through file descriptors
+ * (dup, close, sendmsg) does not change the graph since candidates are
+ * not installed in fds.
+ *
+ * Dequeing a candidate via recvmsg would install it into an fd, but
+ * that takes unix_gc_lock to decrement the inflight count, so it's
+ * serialized with garbage collection.
+ *
+ * MSG_PEEK is special in that it does not change the inflight count,
+ * yet does install the socket into an fd. The following lock/unlock
+ * pair is to ensure serialization with garbage collection. It must be
+ * done between incrementing the file count and installing the file into
+ * an fd.
+ *
+ * If garbage collection starts after the barrier provided by the
+ * lock/unlock, then it will see the elevated refcount and not mark this
+ * as a candidate. If a garbage collection is already in progress
+ * before the file count was incremented, then the lock/unlock pair will
+ * ensure that garbage collection is finished before progressing to
+ * installing the fd.
+ *
+ * (*) A -> B where B is on the queue of A or B is on the queue of C
+ * which is on the queue of listening socket A.
+ */
+ spin_lock(&unix_gc_lock);
+ spin_unlock(&unix_gc_lock);
+}
--
2.26.3