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Subject[34-longterm 143/209] af_unix: limit recursion level
Date
From: Eric Dumazet <eric.dumazet@gmail.com>

=====================================================================
| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|
=====================================================================

commit 25888e30319f8896fc656fc68643e6a078263060 upstream

Its easy to eat all kernel memory and trigger NMI watchdog, using an
exploit program that queues unix sockets on top of others.

lkml ref : http://lkml.org/lkml/2010/11/25/8

This mechanism is used in applications, one choice we have is to have a
recursion limit.

Other limits might be needed as well (if we queue other types of files),
since the passfd mechanism is currently limited by socket receive queue
sizes only.

Add a recursion_level to unix socket, allowing up to 4 levels.

Each time we send an unix socket through sendfd mechanism, we copy its
recursion level (plus one) to receiver. This recursion level is cleared
when socket receive queue is emptied.

[PG: slight modifications required due to absense of 7361c36c5 in 34]

Reported-by: Марк Коренберг <socketpair@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
include/net/af_unix.h | 2 ++
net/unix/af_unix.c | 37 ++++++++++++++++++++++++++++++++-----
net/unix/garbage.c | 2 +-
3 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 1614d78..861045f 100644
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -10,6 +10,7 @@ extern void unix_inflight(struct file *fp);
extern void unix_notinflight(struct file *fp);
extern void unix_gc(void);
extern void wait_for_unix_gc(void);
+extern struct sock *unix_get_socket(struct file *filp);

#define UNIX_HASH_SIZE 256

@@ -56,6 +57,7 @@ struct unix_sock {
spinlock_t lock;
unsigned int gc_candidate : 1;
unsigned int gc_maybe_cycle : 1;
+ unsigned char recursion_level;
wait_queue_head_t peer_wait;
};
#define unix_sk(__sk) ((struct unix_sock *)__sk)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 8c34e3b..207a119 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1324,9 +1324,25 @@ static void unix_destruct_fds(struct sk_buff *skb)
sock_wfree(skb);
}

+#define MAX_RECURSION_LEVEL 4
+
static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
{
int i;
+ unsigned char max_level = 0;
+ int unix_sock_count = 0;
+
+ for (i = scm->fp->count - 1; i >= 0; i--) {
+ struct sock *sk = unix_get_socket(scm->fp->fp[i]);
+
+ if (sk) {
+ unix_sock_count++;
+ max_level = max(max_level,
+ unix_sk(sk)->recursion_level);
+ }
+ }
+ if (unlikely(max_level > MAX_RECURSION_LEVEL))
+ return -ETOOMANYREFS;

/*
* Need to duplicate file references for the sake of garbage
@@ -1337,10 +1353,12 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
if (!UNIXCB(skb).fp)
return -ENOMEM;

- for (i = scm->fp->count-1; i >= 0; i--)
- unix_inflight(scm->fp->fp[i]);
+ if (unix_sock_count) {
+ for (i = scm->fp->count-1; i >= 0; i--)
+ unix_inflight(scm->fp->fp[i]);
+ }
skb->destructor = unix_destruct_fds;
- return 0;
+ return max_level;
}

/*
@@ -1362,6 +1380,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
struct sk_buff *skb;
long timeo;
struct scm_cookie tmp_scm;
+ int max_level = 0;

if (NULL == siocb->scm)
siocb->scm = &tmp_scm;
@@ -1402,8 +1421,9 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
memcpy(UNIXCREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
if (siocb->scm->fp) {
err = unix_attach_fds(siocb->scm, skb);
- if (err)
+ if (err < 0)
goto out_free;
+ max_level = err + 1;
}
unix_get_secdata(siocb->scm, skb);

@@ -1484,6 +1504,8 @@ restart:
}

skb_queue_tail(&other->sk_receive_queue, skb);
+ if (max_level > unix_sk(other)->recursion_level)
+ unix_sk(other)->recursion_level = max_level;
unix_state_unlock(other);
other->sk_data_ready(other, len);
sock_put(other);
@@ -1514,6 +1536,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
int sent = 0;
struct scm_cookie tmp_scm;
bool fds_sent = false;
+ int max_level = 0;

if (NULL == siocb->scm)
siocb->scm = &tmp_scm;
@@ -1578,10 +1601,11 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
/* Only send the fds in the first buffer */
if (siocb->scm->fp && !fds_sent) {
err = unix_attach_fds(siocb->scm, skb);
- if (err) {
+ if (err < 0) {
kfree_skb(skb);
goto out_err;
}
+ max_level = err + 1;
fds_sent = true;
}

@@ -1598,6 +1622,8 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
goto pipe_err_free;

skb_queue_tail(&other->sk_receive_queue, skb);
+ if (max_level > unix_sk(other)->recursion_level)
+ unix_sk(other)->recursion_level = max_level;
unix_state_unlock(other);
other->sk_data_ready(other, size);
sent += size;
@@ -1814,6 +1840,7 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
unix_state_lock(sk);
skb = skb_dequeue(&sk->sk_receive_queue);
if (skb == NULL) {
+ unix_sk(sk)->recursion_level = 0;
if (copied >= target)
goto unlock;

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index ef5aa55..493e0e6 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -96,7 +96,7 @@ static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
unsigned int unix_tot_inflight;


-static struct sock *unix_get_socket(struct file *filp)
+struct sock *unix_get_socket(struct file *filp)
{
struct sock *u_sock = NULL;
struct inode *inode = filp->f_path.dentry->d_inode;
--
1.7.4.4
--
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