Commit 4d231b76 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller

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: default avatarDaniel Borkmann <dborkman@redhat.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 6cd4ce00
......@@ -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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