Messages in this thread Patch in this message | | | From | Paul Gortmaker <> | Subject | [34-longterm 143/209] af_unix: limit recursion level | Date | Thu, 14 Apr 2011 13:55:01 -0400 |
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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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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