tun: fix tun_chr_aio_write so that aio works

aio_write gets const struct iovec * but tun_chr_aio_write casts this to struct
iovec * and modifies the iovec. As a result, attempts to use io_submit
to send packets to a tun device fail with weird errors such as EINVAL.

Since tun is the only user of skb_copy_datagram_from_iovec, we can
fix this simply by changing the later so that it does not
touch the iovec passed to it.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 30 insertions, 17 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 3b513e29d392..589f0ca668d6 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -540,31 +540,34 @@ static inline struct sk_buff *tun_alloc_skb(struct tun_struct *tun,
 
 /* Get packet from user space buffer */
 static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
-                                       struct iovec *iv, size_t count,
+                                       const struct iovec *iv, size_t count,
                                        int noblock)
 {
         struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };
         struct sk_buff *skb;
         size_t len = count, align = 0;
         struct virtio_net_hdr gso = { 0 };
+        int offset = 0;
 
         if (!(tun->flags & TUN_NO_PI)) {
                 if ((len -= sizeof(pi)) > count)
                         return -EINVAL;
 
-                if(memcpy_fromiovec((void *)&pi, iv, sizeof(pi)))
+                if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
                         return -EFAULT;
+                offset += sizeof(pi);
         }
 
         if (tun->flags & TUN_VNET_HDR) {
                 if ((len -= sizeof(gso)) > count)
                         return -EINVAL;
 
-                if (memcpy_fromiovec((void *)&gso, iv, sizeof(gso)))
+                if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
                         return -EFAULT;
 
                 if (gso.hdr_len > len)
                         return -EINVAL;
+                offset += sizeof(pi);
         }
 
         if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
@@ -581,7 +584,7 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
                 return PTR_ERR(skb);
         }
 
-        if (skb_copy_datagram_from_iovec(skb, 0, iv, len)) {
+        if (skb_copy_datagram_from_iovec(skb, 0, iv, offset, len)) {
                 tun->dev->stats.rx_dropped++;
                 kfree_skb(skb);
                 return -EFAULT;
@@ -673,7 +676,7 @@ static ssize_t tun_chr_aio_write(struct kiocb *iocb, const struct iovec *iv,
 
         DBG(KERN_INFO "%s: tun_chr_write %ld\n", tun->dev->name, count);
 
-        result = tun_get_user(tun, (struct iovec *)iv, iov_length(iv, count),
+        result = tun_get_user(tun, iv, iov_length(iv, count),
                               file->f_flags & O_NONBLOCK);
 
         tun_put(tun);
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index af2b21bdda83..1b5c3d298f43 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1715,7 +1715,8 @@ extern int	       skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
                                                         struct iovec *iov);
 extern int             skb_copy_datagram_from_iovec(struct sk_buff *skb,
                                                     int offset,
-                                                    struct iovec *from,
+                                                    const struct iovec *from,
+                                                    int from_offset,
                                                     int len);
 extern int             skb_copy_datagram_const_iovec(const struct sk_buff *from,
                                                      int offset,
diff --git a/include/linux/socket.h b/include/linux/socket.h
index 171b08db9c4f..42a0396f2c59 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -309,8 +309,8 @@ struct ucred {
 
 #ifdef __KERNEL__
 extern int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len);
-extern int memcpy_fromiovecend(unsigned char *kdata, struct iovec *iov, 
-                                int offset, int len);
+extern int memcpy_fromiovecend(unsigned char *kdata, const struct iovec *iov,
+                               int offset, int len);
 extern int csum_partial_copy_fromiovecend(unsigned char *kdata, 
                                           struct iovec *iov, 
                                           int offset, 
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 4dbb05cd572b..914d5fa773b4 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -435,13 +435,15 @@ EXPORT_SYMBOL(skb_copy_datagram_const_iovec);
  *      @skb: buffer to copy
  *      @offset: offset in the buffer to start copying to
  *      @from: io vector to copy to
+ *      @from_offset: offset in the io vector to start copying from
  *      @len: amount of data to copy to buffer from iovec
  *
  *      Returns 0 or -EFAULT.
- *      Note: the iovec is modified during the copy.
+ *      Note: the iovec is not modified during the copy.
  */
 int skb_copy_datagram_from_iovec(struct sk_buff *skb, int offset,
-                                 struct iovec *from, int len)
+                                 const struct iovec *from, int from_offset,
+                                 int len)
 {
         int start = skb_headlen(skb);
         int i, copy = start - offset;
@@ -450,11 +452,12 @@ int skb_copy_datagram_from_iovec(struct sk_buff *skb, int offset,
         if (copy > 0) {
                 if (copy > len)
                         copy = len;
-                if (memcpy_fromiovec(skb->data + offset, from, copy))
+                if (memcpy_fromiovecend(skb->data + offset, from, 0, copy))
                         goto fault;
                 if ((len -= copy) == 0)
                         return 0;
                 offset += copy;
+                from_offset += copy;
         }
 
         /* Copy paged appendix. Hmm... why does this look so complicated? */
@@ -473,8 +476,9 @@ int skb_copy_datagram_from_iovec(struct sk_buff *skb, int offset,
                         if (copy > len)
                                 copy = len;
                         vaddr = kmap(page);
-                        err = memcpy_fromiovec(vaddr + frag->page_offset +
-                                               offset - start, from, copy);
+                        err = memcpy_fromiovecend(vaddr + frag->page_offset +
+                                                  offset - start,
+                                                  from, from_offset, copy);
                         kunmap(page);
                         if (err)
                                 goto fault;
@@ -482,6 +486,7 @@ int skb_copy_datagram_from_iovec(struct sk_buff *skb, int offset,
                         if (!(len -= copy))
                                 return 0;
                         offset += copy;
+                        from_offset += copy;
                 }
                 start = end;
         }
@@ -500,11 +505,14 @@ int skb_copy_datagram_from_iovec(struct sk_buff *skb, int offset,
                                         copy = len;
                                 if (skb_copy_datagram_from_iovec(list,
                                                                  offset - start,
-                                                                 from, copy))
+                                                                 from,
+                                                                 from_offset,
+                                                                 copy))
                                         goto fault;
                                 if ((len -= copy) == 0)
                                         return 0;
                                 offset += copy;
+                                from_offset += copy;
                         }
                         start = end;
                 }
diff --git a/net/core/iovec.c b/net/core/iovec.c
index a215545c0a34..40a76ce19d9f 100644
--- a/net/core/iovec.c
+++ b/net/core/iovec.c
@@ -147,10 +147,11 @@ int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len)
 }
 
 /*
- *      For use with ip_build_xmit
+ *      Copy iovec from kernel. Returns -EFAULT on error.
  */
-int memcpy_fromiovecend(unsigned char *kdata, struct iovec *iov, int offset,
-                        int len)
+
+int memcpy_fromiovecend(unsigned char *kdata, const struct iovec *iov,
+                        int offset, int len)
 {
         /* Skip over the finished iovecs */
         while (offset >= iov->iov_len) {