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Message-ID: <1315488103.2456.16.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date: Thu, 08 Sep 2011 15:21:43 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: sedat.dilek@...il.com
Cc: "Yan, Zheng" <zheng.z.yan@...el.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
"Yan, Zheng" <yanzheng@...n.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"davem@...emloft.net" <davem@...emloft.net>,
"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
"jirislaby@...il.com" <jirislaby@...il.com>,
"Shi, Alex" <alex.shi@...el.com>,
Valdis Kletnieks <Valdis.Kletnieks@...edu>
Subject: [PATCH net-next v3] af_unix: Fix use-after-free crashes
Le jeudi 08 septembre 2011 à 11:59 +0200, Sedat Dilek a écrit :
> I have tested this fixup patch on i386.
> Can we have a separate patch with corrected descriptive text?
>
> Thanks to all involved people.
Here it is :
[PATCH net-next v3] af_unix: Fix use-after-free crashes
Commit 0856a30409 (Scm: Remove unnecessary pid & credential references
in Unix socket's send and receive path) introduced an use-after-free
bug.
We are allowed to steal the references to pid/cred only in the last skb
sent from unix_stream_sendmsg(), because first skbs might be consumed by
the receiver before we finish our sendmsg() call.
Remove scm_release() helper, since its cleaner to clear pid/cred fields
in unix_scm_to_skb() when we steal them.
Based on prior patches from Yan Zheng and Tim Chen
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Reported-by: Jiri Slaby <jirislaby@...il.com>
Tested-by: Sedat Dilek <sedat.dilek@...glemail.com>
Tested-by: Valdis Kletnieks <Valdis.Kletnieks@...edu>
---
include/net/scm.h | 9 ---------
net/unix/af_unix.c | 32 +++++++++++++++++---------------
2 files changed, 17 insertions(+), 24 deletions(-)
diff --git a/include/net/scm.h b/include/net/scm.h
index 68e1e48..2a5b42f 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -78,15 +78,6 @@ static __inline__ void scm_destroy(struct scm_cookie *scm)
__scm_destroy(scm);
}
-static __inline__ void scm_release(struct scm_cookie *scm)
-{
- /* keep ref on pid and cred */
- scm->pid = NULL;
- scm->cred = NULL;
- if (scm->fp)
- __scm_destroy(scm);
-}
-
static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
struct scm_cookie *scm)
{
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e6d9d10..c8a08ba 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1379,15 +1379,18 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
}
static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb,
- bool send_fds, bool ref)
+ bool send_fds, bool steal_refs)
{
int err = 0;
- if (ref) {
+
+ if (!steal_refs) {
UNIXCB(skb).pid = get_pid(scm->pid);
UNIXCB(skb).cred = get_cred(scm->cred);
} else {
UNIXCB(skb).pid = scm->pid;
UNIXCB(skb).cred = scm->cred;
+ scm->pid = NULL;
+ scm->cred = NULL;
}
UNIXCB(skb).fp = NULL;
if (scm->fp && send_fds)
@@ -1454,7 +1457,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
if (skb == NULL)
goto out;
- err = unix_scm_to_skb(siocb->scm, skb, true, false);
+ err = unix_scm_to_skb(siocb->scm, skb, true, true);
if (err < 0)
goto out_free;
max_level = err + 1;
@@ -1550,7 +1553,7 @@ restart:
unix_state_unlock(other);
other->sk_data_ready(other, len);
sock_put(other);
- scm_release(siocb->scm);
+ scm_destroy(siocb->scm);
return len;
out_unlock:
@@ -1577,6 +1580,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
int sent = 0;
struct scm_cookie tmp_scm;
bool fds_sent = false;
+ bool steal_refs = false;
int max_level;
if (NULL == siocb->scm)
@@ -1638,11 +1642,14 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
size = min_t(int, size, skb_tailroom(skb));
- /* 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 first buffer
+ * Last buffer can steal our references to pid/cred
+ */
+ steal_refs = (sent + size >= len);
+ err = unix_scm_to_skb(siocb->scm, skb, !fds_sent, steal_refs);
if (err < 0) {
kfree_skb(skb);
- goto out;
+ goto out_err;
}
max_level = err + 1;
fds_sent = true;
@@ -1650,7 +1657,7 @@ 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 +1674,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
sent += size;
}
- if (skb)
- scm_release(siocb->scm);
- else
- scm_destroy(siocb->scm);
+ scm_destroy(siocb->scm);
siocb->scm = NULL;
return sent;
@@ -1683,9 +1687,7 @@ pipe_err:
send_sig(SIGPIPE, current, 0);
err = -EPIPE;
out_err:
- if (skb == NULL)
- scm_destroy(siocb->scm);
-out:
+ scm_destroy(siocb->scm);
siocb->scm = NULL;
return sent ? : err;
}
--
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