From: Arjun Roy arjunroy@google.com
[ Upstream commit 70701b83e208767f2720d8cd3e6a62cddafb3a30 ]
TCP Receive zerocopy iterates through the SKB queue via tcp_recv_skb(), acquiring a pointer to an SKB and an offset within that SKB to read from. From there, it iterates the SKB frags array to determine which offset to start remapping pages from.
However, this is built on the assumption that the offset read so far within the SKB is smaller than the SKB length. If this assumption is violated, we can attempt to read an invalid frags array element, which would cause a fault.
tcp_recv_skb() can cause such an SKB to be returned when the TCP FIN flag is set. Therefore, we must guard against this occurrence inside skb_advance_frag().
One way that we can reproduce this error follows: 1) In a receiver program, call getsockopt(TCP_ZEROCOPY_RECEIVE) with: char some_array[32 * 1024]; struct tcp_zerocopy_receive zc = { .copybuf_address = (__u64) &some_array[0], .copybuf_len = 32 * 1024, };
2) In a sender program, after a TCP handshake, send the following sequence of packets: i) Seq = [X, X+4000] ii) Seq = [X+4000, X+5000] iii) Seq = [X+4000, X+5000], Flags = FIN | URG, urgptr=1000
(This can happen without URG, if we have a signal pending, but URG is a convenient way to reproduce the behaviour).
In this case, the following event sequence will occur on the receiver:
tcp_zerocopy_receive(): -> receive_fallback_to_copy() // copybuf_len >= inq -> tcp_recvmsg_locked() // reads 5000 bytes, then breaks due to URG -> tcp_recv_skb() // yields skb with skb->len == offset -> tcp_zerocopy_set_hint_for_skb() -> skb_advance_to_frag() // will returns a frags ptr. >= nr_frags -> find_next_mappable_frag() // will dereference this bad frags ptr.
With this patch, skb_advance_to_frag() will no longer return an invalid frags pointer, and will return NULL instead, fixing the issue.
Signed-off-by: Arjun Roy arjunroy@google.com Signed-off-by: Eric Dumazet edumazet@google.com Fixes: 05255b823a61 ("tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive") Link: https://lore.kernel.org/r/20211111235215.2605384-1-arjunroy.kdev@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 8affba5909bdf..844c6e5a82891 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1776,6 +1776,9 @@ static skb_frag_t *skb_advance_to_frag(struct sk_buff *skb, u32 offset_skb, { skb_frag_t *frag;
+ if (unlikely(offset_skb >= skb->len)) + return NULL; + offset_skb -= skb_headlen(skb); if ((int)offset_skb < 0 || skb_has_frag_list(skb)) return NULL;