unix: properly account for FDs passed over unix sockets (CVE-2013-4312)

3 files changed, 145 insertions, 0 deletions

diff --git a/debian/changelog b/debian/changelog
index f93cd4a7398f..f342fd7a8197 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,5 +1,6 @@
 linux (4.3.3-6) UNRELEASED; urgency=medium
 
+  [ Ben Hutchings ]
   * debian.py: Implement stable order of fields in debian/tests/control
   * debian.py: Implement stable order of fields not in the predefined order
   * genorig.py: Make orig tarballs really reproducible:
@@ -18,6 +19,9 @@ linux (4.3.3-6) UNRELEASED; urgency=medium
   * block/sd: Fix device-imposed transfer length limits (Closes: #805252)
   * [x86] drm/vmwgfx: Fix a width / pitch mismatch on framebuffer updates
 
+  [ Salvatore Bonaccorso ]
+  * unix: properly account for FDs passed over unix sockets (CVE-2013-4312)
+
  -- Ben Hutchings <ben@decadent.org.uk>  Fri, 08 Jan 2016 12:08:13 +0000
 
 linux (4.3.3-5) unstable; urgency=medium
diff --git a/debian/patches/bugfix/all/unix-properly-account-for-FDs-passed-over-unix-socke.patch b/debian/patches/bugfix/all/unix-properly-account-for-FDs-passed-over-unix-socke.patch
new file mode 100644
index 000000000000..8cd6bb4ace1a
--- /dev/null
+++ b/debian/patches/bugfix/all/unix-properly-account-for-FDs-passed-over-unix-socke.patch
@@ -0,0 +1,140 @@
+From: willy tarreau <w@1wt.eu>
+Date: Sun, 10 Jan 2016 07:54:56 +0100
+Subject: unix: properly account for FDs passed over unix sockets
+Origin: https://git.kernel.org/linus/712f4aad406bb1ed67f3f98d04c044191f0ff593
+
+It is possible for a process to allocate and accumulate far more FDs than
+the process' limit by sending them over a unix socket then closing them
+to keep the process' fd count low.
+
+This change addresses this problem by keeping track of the number of FDs
+in flight per user and preventing non-privileged processes from having
+more FDs in flight than their configured FD limit.
+
+Reported-by: socketpair@gmail.com
+Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
+Mitigates: CVE-2013-4312 (Linux 2.0+)
+Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
+Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
+Signed-off-by: Willy Tarreau <w@1wt.eu>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ include/linux/sched.h |  1 +
+ net/unix/af_unix.c    | 24 ++++++++++++++++++++----
+ net/unix/garbage.c    | 13 ++++++++-----
+ 3 files changed, 29 insertions(+), 9 deletions(-)
+
+diff --git a/include/linux/sched.h b/include/linux/sched.h
+index edad7a4..fbf25f1 100644
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -830,6 +830,7 @@ struct user_struct {
+ 	unsigned long mq_bytes;	/* How many bytes can be allocated to mqueue? */
+ #endif
+ 	unsigned long locked_shm; /* How many pages of mlocked shm ? */
++	unsigned long unix_inflight;	/* How many files in flight in unix sockets */
+ 
+ #ifdef CONFIG_KEYS
+ 	struct key *uid_keyring;	/* UID specific keyring */
+diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
+index ef05cd9..e3f85bc 100644
+--- a/net/unix/af_unix.c
++++ b/net/unix/af_unix.c
+@@ -1513,6 +1513,21 @@ static void unix_destruct_scm(struct sk_buff *skb)
+ 	sock_wfree(skb);
+ }
+ 
++/*
++ * The "user->unix_inflight" variable is protected by the garbage
++ * collection lock, and we just read it locklessly here. If you go
++ * over the limit, there might be a tiny race in actually noticing
++ * it across threads. Tough.
++ */
++static inline bool too_many_unix_fds(struct task_struct *p)
++{
++	struct user_struct *user = current_user();
++
++	if (unlikely(user->unix_inflight > task_rlimit(p, RLIMIT_NOFILE)))
++		return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
++	return false;
++}
++
+ #define MAX_RECURSION_LEVEL 4
+ 
+ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
+@@ -1521,6 +1536,9 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
+ 	unsigned char max_level = 0;
+ 	int unix_sock_count = 0;
+ 
++	if (too_many_unix_fds(current))
++		return -ETOOMANYREFS;
++
+ 	for (i = scm->fp->count - 1; i >= 0; i--) {
+ 		struct sock *sk = unix_get_socket(scm->fp->fp[i]);
+ 
+@@ -1542,10 +1560,8 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
+ 	if (!UNIXCB(skb).fp)
+ 		return -ENOMEM;
+ 
+-	if (unix_sock_count) {
+-		for (i = scm->fp->count - 1; i >= 0; i--)
+-			unix_inflight(scm->fp->fp[i]);
+-	}
++	for (i = scm->fp->count - 1; i >= 0; i--)
++		unix_inflight(scm->fp->fp[i]);
+ 	return max_level;
+ }
+ 
+diff --git a/net/unix/garbage.c b/net/unix/garbage.c
+index a73a226..8fcdc22 100644
+--- a/net/unix/garbage.c
++++ b/net/unix/garbage.c
+@@ -120,11 +120,11 @@ void unix_inflight(struct file *fp)
+ {
+ 	struct sock *s = unix_get_socket(fp);
+ 
++	spin_lock(&unix_gc_lock);
++
+ 	if (s) {
+ 		struct unix_sock *u = unix_sk(s);
+ 
+-		spin_lock(&unix_gc_lock);
+-
+ 		if (atomic_long_inc_return(&u->inflight) == 1) {
+ 			BUG_ON(!list_empty(&u->link));
+ 			list_add_tail(&u->link, &gc_inflight_list);
+@@ -132,25 +132,28 @@ void unix_inflight(struct file *fp)
+ 			BUG_ON(list_empty(&u->link));
+ 		}
+ 		unix_tot_inflight++;
+-		spin_unlock(&unix_gc_lock);
+ 	}
++	fp->f_cred->user->unix_inflight++;
++	spin_unlock(&unix_gc_lock);
+ }
+ 
+ void unix_notinflight(struct file *fp)
+ {
+ 	struct sock *s = unix_get_socket(fp);
+ 
++	spin_lock(&unix_gc_lock);
++
+ 	if (s) {
+ 		struct unix_sock *u = unix_sk(s);
+ 
+-		spin_lock(&unix_gc_lock);
+ 		BUG_ON(list_empty(&u->link));
+ 
+ 		if (atomic_long_dec_and_test(&u->inflight))
+ 			list_del_init(&u->link);
+ 		unix_tot_inflight--;
+-		spin_unlock(&unix_gc_lock);
+ 	}
++	fp->f_cred->user->unix_inflight--;
++	spin_unlock(&unix_gc_lock);
+ }
+ 
+ static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
+-- 
+2.7.0.rc3
+
diff --git a/debian/patches/series b/debian/patches/series
index ad076a3f14fc..64d5a76f6218 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -138,3 +138,4 @@ bugfix/all/usb-serial-visor-fix-crash-on-detecting-device-without-write_urbs.pat
 bugfix/all/tty-fix-unsafe-ldisc-reference-via-ioctl-tiocgetd.patch
 bugfix/all/block-sd-fix-device-imposed-transfer-length-limits.patch
 bugfix/x86/drm-vmwgfx-fix-a-width-pitch-mismatch-on-framebuffer.patch
+bugfix/all/unix-properly-account-for-FDs-passed-over-unix-socke.patch