diff options
| author | Eric Dumazet <edumazet@google.com> | 2015-12-14 14:08:53 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2015-12-14 23:52:00 -0500 |
| commit | 5037e9ef9454917b047f9f3a19b4dd179fbf7cd4 (patch) | |
| tree | dc12a109e95664b9b2d3f0dbbf97f195c57595f0 /include/net/sock.h | |
| parent | 2274d3753f6c5a885be4cfdf8b39ae2045ba6e30 (diff) | |
net: fix IP early demux races
David Wilder reported crashes caused by dst reuse.
<quote David>
I am seeing a crash on a distro V4.2.3 kernel caused by a double
release of a dst_entry. In ipv4_dst_destroy() the call to
list_empty() finds a poisoned next pointer, indicating the dst_entry
has already been removed from the list and freed. The crash occurs
18 to 24 hours into a run of a network stress exerciser.
</quote>
Thanks to his detailed report and analysis, we were able to understand
the core issue.
IP early demux can associate a dst to skb, after a lookup in TCP/UDP
sockets.
When socket cache is not properly set, we want to store into
sk->sk_dst_cache the dst for future IP early demux lookups,
by acquiring a stable refcount on the dst.
Problem is this acquisition is simply using an atomic_inc(),
which works well, unless the dst was queued for destruction from
dst_release() noticing dst refcount went to zero, if DST_NOCACHE
was set on dst.
We need to make sure current refcount is not zero before incrementing
it, or risk double free as David reported.
This patch, being a stable candidate, adds two new helpers, and use
them only from IP early demux problematic paths.
It might be possible to merge in net-next skb_dst_force() and
skb_dst_force_safe(), but I prefer having the smallest patch for stable
kernels : Maybe some skb_dst_force() callers do not expect skb->dst
can suddenly be cleared.
Can probably be backported back to linux-3.6 kernels
Reported-by: David J. Wilder <dwilder@us.ibm.com>
Tested-by: David J. Wilder <dwilder@us.ibm.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/sock.h')
| -rw-r--r-- | include/net/sock.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/net/sock.h b/include/net/sock.h index c4205e0a3a2d..28790fe18206 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -817,7 +817,7 @@ void sk_stream_write_space(struct sock *sk); static inline void __sk_add_backlog(struct sock *sk, struct sk_buff *skb) { /* dont let skb dst not refcounted, we are going to leave rcu lock */ - skb_dst_force(skb); + skb_dst_force_safe(skb); if (!sk->sk_backlog.tail) sk->sk_backlog.head = skb; |