[linux] 04/04: tcp: fix use after free in tcp_xmit_retransmit_queue() (CVE-2016-6828)

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benh pushed a commit to branch wheezy-security
in repository linux.

commit 241e314e71df6c031f2f92d7db8942d4672ca04a
Author: Ben Hutchings <ben at decadent.org.uk>
Date:   Tue Aug 30 13:05:18 2016 +0100

    tcp: fix use after free in tcp_xmit_retransmit_queue() (CVE-2016-6828)
---
 debian/changelog                                   |  1 +
 ...e-after-free-in-tcp_xmit_retransmit_queue.patch | 50 ++++++++++++++++++++++
 debian/patches/series                              |  1 +
 3 files changed, 52 insertions(+)

diff --git a/debian/changelog b/debian/changelog
index 021dad9..ee1a74d 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -13,6 +13,7 @@ linux (3.2.81-2) UNRELEASED; urgency=medium
     - [x86] Fix an RT MCE crash
   * [arm*] oabi compat: add missing access checks (CVE-2016-3857)
   * aacraid: Check size values after double-fetch from user (CVE-2016-6480)
+  * tcp: fix use after free in tcp_xmit_retransmit_queue() (CVE-2016-6828)
 
  -- Ben Hutchings <ben at decadent.org.uk>  Fri, 17 Jun 2016 23:35:41 +0100
 
diff --git a/debian/patches/bugfix/all/tcp-fix-use-after-free-in-tcp_xmit_retransmit_queue.patch b/debian/patches/bugfix/all/tcp-fix-use-after-free-in-tcp_xmit_retransmit_queue.patch
new file mode 100644
index 0000000..19b6906
--- /dev/null
+++ b/debian/patches/bugfix/all/tcp-fix-use-after-free-in-tcp_xmit_retransmit_queue.patch
@@ -0,0 +1,50 @@
+From: Eric Dumazet <edumazet at google.com>
+Date: Wed, 17 Aug 2016 05:56:26 -0700
+Subject: tcp: fix use after free in tcp_xmit_retransmit_queue()
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+Origin: https://git.kernel.org/linus/bb1fceca22492109be12640d49f5ea5a544c6bb4
+
+When tcp_sendmsg() allocates a fresh and empty skb, it puts it at the
+tail of the write queue using tcp_add_write_queue_tail()
+
+Then it attempts to copy user data into this fresh skb.
+
+If the copy fails, we undo the work and remove the fresh skb.
+
+Unfortunately, this undo lacks the change done to tp->highest_sack and
+we can leave a dangling pointer (to a freed skb)
+
+Later, tcp_xmit_retransmit_queue() can dereference this pointer and
+access freed memory. For regular kernels where memory is not unmapped,
+this might cause SACK bugs because tcp_highest_sack_seq() is buggy,
+returning garbage instead of tp->snd_nxt, but with various debug
+features like CONFIG_DEBUG_PAGEALLOC, this can crash the kernel.
+
+This bug was found by Marco Grassi thanks to syzkaller.
+
+Fixes: 6859d49475d4 ("[TCP]: Abstract tp->highest_sack accessing & point to next skb")
+Reported-by: Marco Grassi <marco.gra at gmail.com>
+Signed-off-by: Eric Dumazet <edumazet at google.com>
+Cc: Ilpo Järvinen <ilpo.jarvinen at helsinki.fi>
+Cc: Yuchung Cheng <ycheng at google.com>
+Cc: Neal Cardwell <ncardwell at google.com>
+Acked-by: Neal Cardwell <ncardwell at google.com>
+Reviewed-by: Cong Wang <xiyou.wangcong at gmail.com>
+Signed-off-by: David S. Miller <davem at davemloft.net>
+---
+ include/net/tcp.h | 2 ++
+ 1 file changed, 2 insertions(+)
+
+--- a/include/net/tcp.h
++++ b/include/net/tcp.h
+@@ -1293,6 +1293,8 @@ static inline void tcp_check_send_head(s
+ {
+ 	if (sk->sk_send_head == skb_unlinked)
+ 		sk->sk_send_head = NULL;
++	if (tcp_sk(sk)->highest_sack == skb_unlinked)
++		tcp_sk(sk)->highest_sack = NULL;
+ }
+ 
+ static inline void tcp_init_send_head(struct sock *sk)
diff --git a/debian/patches/series b/debian/patches/series
index a338bba..19fe7c6 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -1120,6 +1120,7 @@ bugfix/all/tcp-make-challenge-acks-less-predictable.patch
 bugfix/all/audit-fix-a-double-fetch-in-audit_log_single_execve_arg.patch
 bugfix/arm/arm-oabi-compat-add-missing-access-checks.patch
 bugfix/all/aacraid-check-size-values-after-double-fetch-from-us.patch
+bugfix/all/tcp-fix-use-after-free-in-tcp_xmit_retransmit_queue.patch
 
 # ABI maintenance
 debian/perf-hide-abi-change-in-3.2.30.patch

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