Commit 4d231b76 authored Dec 30, 2013 by Daniel Borkmann Committed by David S. Miller Jan 02, 2014

net: llc: fix use after free in llc_ui_recvmsg



While commit 30a584d9 fixes datagram interface in LLC, a use
after free bug has been introduced for SOCK_STREAM sockets that do
not make use of MSG_PEEK.

The flow is as follow ...

  if (!(flags & MSG_PEEK)) {
    ...
    sk_eat_skb(sk, skb, false);
    ...
  }
  ...
  if (used + offset < skb->len)
    continue;

... where sk_eat_skb() calls __kfree_skb(). Therefore, cache
original length and work on skb_len to check partial reads.

Fixes: 30a584d9 ("[LLX]: SOCK_DGRAM interface fixes")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 6cd4ce00

net/llc/af_llc.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -715,7 +715,7 @@ static int llc_ui_recvmsg(struct kiocb iocb, struct socket sock,
		unsigned long cpu_flags;
		size_t copied = 0;
		u32 peek_seq = 0;
		u32 *seq;
		u32 *seq, skb_len;
		unsigned long used;
		int target; /* Read at least this many bytes */
		long timeo;
		@@ -812,6 +812,7 @@ static int llc_ui_recvmsg(struct kiocb iocb, struct socket sock,
		}
		continue;
		found_ok_skb:
		skb_len = skb->len;
		/* Ok so how much can we use? */
		used = skb->len - offset;
		if (len < used)
		@@ -844,7 +845,7 @@ static int llc_ui_recvmsg(struct kiocb iocb, struct socket sock,
		}

		/* Partial read */
		if (used + offset < skb->len)
		if (used + offset < skb_len)
		continue;
		} while (len > 0);

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