[PATCH] Fix 32bit sendmsg() flaw

When we copy 32bit ->msg_control contents to kernel, we walk the same
userland data twice without sanity checks on the second pass.

Second version of this patch: the original broke with 64-bit arches
running 32-bit-compat-mode executables doing sendmsg() syscalls with
unaligned CMSG data areas

Another thing is that we use kmalloc() to allocate and sock_kfree_s()
to free afterwards; less serious, but also needs fixing.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 26 insertions, 18 deletions

diff --git a/net/compat.c b/net/compat.c
index d99ab9695893..e593dace2fdb 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -135,13 +135,14 @@ static inline struct compat_cmsghdr __user *cmsg_compat_nxthdr(struct msghdr *ms
  * thus placement) of cmsg headers and length are different for
  * 32-bit apps.  -DaveM
  */
-int cmsghdr_from_user_compat_to_kern(struct msghdr *kmsg,
+int cmsghdr_from_user_compat_to_kern(struct msghdr *kmsg, struct sock *sk,
                                unsigned char *stackbuf, int stackbuf_size)
 {
         struct compat_cmsghdr __user *ucmsg;
         struct cmsghdr *kcmsg, *kcmsg_base;
         compat_size_t ucmlen;
         __kernel_size_t kcmlen, tmp;
+        int err = -EFAULT;
 
         kcmlen = 0;
         kcmsg_base = kcmsg = (struct cmsghdr *)stackbuf;
@@ -156,6 +157,7 @@ int cmsghdr_from_user_compat_to_kern(struct msghdr *kmsg,
 
                 tmp = ((ucmlen - CMSG_COMPAT_ALIGN(sizeof(*ucmsg))) +
                        CMSG_ALIGN(sizeof(struct cmsghdr)));
+                tmp = CMSG_ALIGN(tmp);
                 kcmlen += tmp;
                 ucmsg = cmsg_compat_nxthdr(kmsg, ucmsg, ucmlen);
         }
@@ -167,30 +169,34 @@ int cmsghdr_from_user_compat_to_kern(struct msghdr *kmsg,
          * until we have successfully copied over all of the data
          * from the user.
          */
-        if(kcmlen > stackbuf_size)
-                kcmsg_base = kcmsg = kmalloc(kcmlen, GFP_KERNEL);
-        if(kcmsg == NULL)
+        if (kcmlen > stackbuf_size)
+                kcmsg_base = kcmsg = sock_kmalloc(sk, kcmlen, GFP_KERNEL);
+        if (kcmsg == NULL)
                 return -ENOBUFS;
 
         /* Now copy them over neatly. */
         memset(kcmsg, 0, kcmlen);
         ucmsg = CMSG_COMPAT_FIRSTHDR(kmsg);
         while(ucmsg != NULL) {
-                __get_user(ucmlen, &ucmsg->cmsg_len);
+                if (__get_user(ucmlen, &ucmsg->cmsg_len))
+                        goto Efault;
+                if (!CMSG_COMPAT_OK(ucmlen, ucmsg, kmsg))
+                        goto Einval;
                 tmp = ((ucmlen - CMSG_COMPAT_ALIGN(sizeof(*ucmsg))) +
                        CMSG_ALIGN(sizeof(struct cmsghdr)));
+                if ((char *)kcmsg_base + kcmlen - (char *)kcmsg < CMSG_ALIGN(tmp))
+                        goto Einval;
                 kcmsg->cmsg_len = tmp;
-                __get_user(kcmsg->cmsg_level, &ucmsg->cmsg_level);
-                __get_user(kcmsg->cmsg_type, &ucmsg->cmsg_type);
-
-                /* Copy over the data. */
-                if(copy_from_user(CMSG_DATA(kcmsg),
-                                  CMSG_COMPAT_DATA(ucmsg),
-                                  (ucmlen - CMSG_COMPAT_ALIGN(sizeof(*ucmsg)))))
-                        goto out_free_efault;
+                tmp = CMSG_ALIGN(tmp);
+                if (__get_user(kcmsg->cmsg_level, &ucmsg->cmsg_level) ||
+                    __get_user(kcmsg->cmsg_type, &ucmsg->cmsg_type) ||
+                    copy_from_user(CMSG_DATA(kcmsg),
+                                   CMSG_COMPAT_DATA(ucmsg),
+                                   (ucmlen - CMSG_COMPAT_ALIGN(sizeof(*ucmsg)))))
+                        goto Efault;
 
                 /* Advance. */
-                kcmsg = (struct cmsghdr *)((char *)kcmsg + CMSG_ALIGN(tmp));
+                kcmsg = (struct cmsghdr *)((char *)kcmsg + tmp);
                 ucmsg = cmsg_compat_nxthdr(kmsg, ucmsg, ucmlen);
         }
 
@@ -199,10 +205,12 @@ int cmsghdr_from_user_compat_to_kern(struct msghdr *kmsg,
         kmsg->msg_controllen = kcmlen;
         return 0;
 
-out_free_efault:
-        if(kcmsg_base != (struct cmsghdr *)stackbuf)
-                kfree(kcmsg_base);
-        return -EFAULT;
+Einval:
+        err = -EINVAL;
+Efault:
+        if (kcmsg_base != (struct cmsghdr *)stackbuf)
+                sock_kfree_s(sk, kcmsg_base, kcmlen);
+        return err;
 }
 
 int put_cmsg_compat(struct msghdr *kmsg, int level, int type, int len, void *data)