econet: fix CVE-2010-3848

Don't declare variable sized array of iovecs on the stack since this
could cause stack overflow if msg->msgiovlen is large.  Instead, coalesce
the user-supplied data into a new buffer and use a single iovec for it.

Signed-off-by: Phil Blundell <philb@gnu.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/econet/af_econet.c b/net/econet/af_econet.c
index d41ba8e..13992e1 100644 (file)
--- a/net/econet/af_econet.c
+++ b/net/econet/af_econet.c
@@ -31,6 +31,7 @@
 #include <linux/skbuff.h>
 #include <linux/udp.h>
 #include <linux/slab.h>
+#include <linux/vmalloc.h>
 #include <net/sock.h>
 #include <net/inet_common.h>
 #include <linux/stat.h>
@@ -276,12 +277,12 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
 #endif
 #ifdef CONFIG_ECONET_AUNUDP
        struct msghdr udpmsg;
-       struct iovec iov[msg->msg_iovlen+1];
+       struct iovec iov[2];
        struct aunhdr ah;
        struct sockaddr_in udpdest;
        __kernel_size_t size;
-       int i;
        mm_segment_t oldfs;
+       char *userbuf;
 #endif
 
        /*
@@ -319,17 +320,17 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
                }
        }
 
-       if (len + 15 > dev->mtu) {
-               mutex_unlock(&econet_mutex);
-               return -EMSGSIZE;
-       }
-
        if (dev->type == ARPHRD_ECONET) {
                /* Real hardware Econet.  We're not worthy etc. */
 #ifdef CONFIG_ECONET_NATIVE
                unsigned short proto = 0;
                int res;
 
+               if (len + 15 > dev->mtu) {
+                       mutex_unlock(&econet_mutex);
+                       return -EMSGSIZE;
+               }
+
                dev_hold(dev);
 
                skb = sock_alloc_send_skb(sk, len+LL_ALLOCATED_SPACE(dev),
@@ -405,6 +406,11 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
                return -ENETDOWN;               /* No socket - can't send */
        }
 
+       if (len > 32768) {
+               err = -E2BIG;
+               goto error;
+       }
+
        /* Make up a UDP datagram and hand it off to some higher intellect. */
 
        memset(&udpdest, 0, sizeof(udpdest));
@@ -436,36 +442,26 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
 
        /* tack our header on the front of the iovec */
        size = sizeof(struct aunhdr);
-       /*
-        * XXX: that is b0rken.  We can't mix userland and kernel pointers
-        * in iovec, since on a lot of platforms copy_from_user() will
-        * *not* work with the kernel and userland ones at the same time,
-        * regardless of what we do with set_fs().  And we are talking about
-        * econet-over-ethernet here, so "it's only ARM anyway" doesn't
-        * apply.  Any suggestions on fixing that code?         -- AV
-        */
        iov[0].iov_base = (void *)&ah;
        iov[0].iov_len = size;
-       for (i = 0; i < msg->msg_iovlen; i++) {
-               void __user *base = msg->msg_iov[i].iov_base;
-               size_t iov_len = msg->msg_iov[i].iov_len;
-               /* Check it now since we switch to KERNEL_DS later. */
-               if (!access_ok(VERIFY_READ, base, iov_len)) {
-                       mutex_unlock(&econet_mutex);
-                       return -EFAULT;
-               }
-               iov[i+1].iov_base = base;
-               iov[i+1].iov_len = iov_len;
-               size += iov_len;
+
+       userbuf = vmalloc(len);
+       if (userbuf == NULL) {
+               err = -ENOMEM;
+               goto error;
        }
 
+       iov[1].iov_base = userbuf;
+       iov[1].iov_len = len;
+       err = memcpy_fromiovec(userbuf, msg->msg_iov, len);
+       if (err)
+               goto error_free_buf;
+
        /* Get a skbuff (no data, just holds our cb information) */
        if ((skb = sock_alloc_send_skb(sk, 0,
                                       msg->msg_flags & MSG_DONTWAIT,
-                                      &err)) == NULL) {
-               mutex_unlock(&econet_mutex);
-               return err;
-       }
+                                      &err)) == NULL)
+               goto error_free_buf;
 
        eb = (struct ec_cb *)&skb->cb;
 
@@ -481,7 +477,7 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
        udpmsg.msg_name = (void *)&udpdest;
        udpmsg.msg_namelen = sizeof(udpdest);
        udpmsg.msg_iov = &iov[0];
-       udpmsg.msg_iovlen = msg->msg_iovlen + 1;
+       udpmsg.msg_iovlen = 2;
        udpmsg.msg_control = NULL;
        udpmsg.msg_controllen = 0;
        udpmsg.msg_flags=0;
@@ -489,9 +485,13 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
        oldfs = get_fs(); set_fs(KERNEL_DS);    /* More privs :-) */
        err = sock_sendmsg(udpsock, &udpmsg, size);
        set_fs(oldfs);
+
+error_free_buf:
+       vfree(userbuf);
 #else
        err = -EPROTOTYPE;
 #endif
+       error:
        mutex_unlock(&econet_mutex);
 
        return err;