[PATCH -next] unix stream: Fix use-after-free crashes
DORMANTno replies
REVIEWED: 1 (0M)
From: Yan, Zheng <hidden>
Date: 2011-09-03 16:25:11
Subsystem:
networking [general], networking [unix sockets], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Kuniyuki Iwashima, Linus Torvalds
1 review trailer.
Commit 0856a30409 (Scm: Remove unnecessary pid & credential references in Unix socket's send and receive path) introduced a use-after-free bug. It happens that if skb is consumed and destructed by the receive side before unix_stream_sendmsg finishes its job. Signed-off-by: Zheng Yan <redacted> Reported-by: Jiri Slaby <redacted> Tested-by: Sedat Dilek <redacted> ---
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e6d9d10..70cf1f9 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c@@ -1577,6 +1577,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock, int sent = 0; struct scm_cookie tmp_scm; bool fds_sent = false; + bool scm_ref = true; int max_level; if (NULL == siocb->scm)
@@ -1637,12 +1638,21 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock, */ size = min_t(int, size, skb_tailroom(skb)); + /* + * If a single skb is large enough to hold all data, pass the + * scm reference to the skb. Otherwise we should hold a scm + * reference because the skb can be consumed at any time after + * we queue it into sk_receive_queue. + */ + if (!fds_sent && sent + size >= len) + scm_ref = false; - /* Only send the fds and no ref to pid in the first buffer */ - err = unix_scm_to_skb(siocb->scm, skb, !fds_sent, fds_sent); + /* Only send the fds in the first buffer */ + err = unix_scm_to_skb(siocb->scm, skb, !fds_sent, + fds_sent || scm_ref); if (err < 0) { kfree_skb(skb); - goto out; + goto out_err; } max_level = err + 1; fds_sent = true;
@@ -1650,7 +1660,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock, err = memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size); if (err) { kfree_skb(skb); - goto out; + goto out_err; } unix_state_lock(other);
@@ -1667,10 +1677,10 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock, sent += size; } - if (skb) - scm_release(siocb->scm); - else + if (scm_ref) scm_destroy(siocb->scm); + else + scm_release(siocb->scm); siocb->scm = NULL; return sent;
@@ -1683,9 +1693,10 @@ pipe_err: send_sig(SIGPIPE, current, 0); err = -EPIPE; out_err: - if (skb == NULL) + if (scm_ref) scm_destroy(siocb->scm); -out: + else + scm_release(siocb->scm); siocb->scm = NULL; return sent ? : err; }