tcp: fix use after free in tcp_xmit_retransmit_queue()
authorEric Dumazet <edumazet@google.com>
Wed, 17 Aug 2016 12:56:26 +0000 (05:56 -0700)
committermobile promotions <svcmobile_promotions@nvidia.com>
Mon, 28 Nov 2016 17:26:18 +0000 (09:26 -0800)
commit0c20962647685008dfc6a15fb8a2169ed2abafe6
treebce2e207e8e930b76709b581de553b3edd090f19
parent3c15c37dc613cb75339f8e0d546ab30643e65b84
tcp: fix use after free in tcp_xmit_retransmit_queue()

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.

Bug 1823317

Change-Id: I9bf709b21e5637f338c34d894617f33d84f93ecc
Fixes: 6859d49475d4 ("[TCP]: Abstract tp->highest_sack accessing & point to next skb")
Reported-by: Marco Grassi <marco.gra@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Gagan Grover <ggrover@nvidia.com>
Reviewed-on: http://git-master/r/1260003
GVS: Gerrit_Virtual_Submit
Reviewed-by: Vinayak Pane <vpane@nvidia.com>
include/net/tcp.h