[repost with netdev added - hadn't realized it wasn't in Cc]
On Tue, Aug 09, 2016 at 03:58:36PM +0100, Al Viro wrote:
> Actually returning to the original behaviour would be "restore ->msg_iter
> if we tried skb_copy_and_csum_datagram() and failed for any reason". Which
> would be bloody inconsistent wrt EFAULT, since the other branch (chunk
> large enough to cover the entire recvmsg()) will copy as much as it can
> and (in old kernel) drain iovec or (on the current one) leave iov_iter
> advance unreverted.
To resurrect the old thread: the problem is still there. Namely, csum
mismatch on packet should leave the iterator as it had been. That much
is clear; the question is what should be done on EFAULT halfway through.
Semantics of both csum and non-csum skb_copy_datagram_msg() variants in
EFAULT case is an interesting question. None of that family report
partial copy; it's full or -EFAULT. So for the sake of basic sanity
it would be better to leave iterator in the original state when that
kind of thing happens. On the other hand, quite a few callers don't
care about the state of iterator after that and I wonder if the overhead
would be sensitive. OTTH, the overhead in question is "save 5 words into
local variable and don't use it in the normal case" - in the code that
copies an skb worth of data.
AFAICS, the following gives consistent (and minimally surprising) semantics,
as well as fixing the outright bug with iov_iter left advanced in case of csum
errors. Comments?
diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index c27011bbe30c..14ae17e77603 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -848,7 +848,7 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
vlan_offset = offsetof(struct vlan_ethhdr, h_vlan_proto);
total += VLAN_HLEN;
- ret = skb_copy_datagram_iter(skb, 0, iter, vlan_offset);
+ ret = __skb_copy_datagram_iter(skb, 0, iter, vlan_offset);
if (ret || !iov_iter_count(iter))
goto done;
@@ -857,7 +857,7 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
goto done;
}
- ret = skb_copy_datagram_iter(skb, vlan_offset, iter,
+ ret = __skb_copy_datagram_iter(skb, vlan_offset, iter,
skb->len - vlan_offset);
done:
@@ -899,11 +899,14 @@ static ssize_t macvtap_do_read(struct macvtap_queue *q,
finish_wait(sk_sleep(&q->sk), &wait);
if (skb) {
+ struct iov_iter saved = *to;
ret = macvtap_put_user(q, skb, to);
- if (unlikely(ret < 0))
+ if (unlikely(ret < 0)) {
+ *to = saved;
kfree_skb(skb);
- else
+ } else {
consume_skb(skb);
+ }
}
return ret;
}
diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index a411b43a69eb..0d8badc3c4e9 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -480,7 +480,7 @@ static ssize_t ppp_read(struct file *file, char __user *buf,
iov.iov_base = buf;
iov.iov_len = count;
iov_iter_init(&to, READ, &iov, 1, count);
- if (skb_copy_datagram_iter(skb, 0, &to, skb->len))
+ if (__skb_copy_datagram_iter(skb, 0, &to, skb->len))
goto outf;
ret = skb->len;
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 30863e378925..2003b8c9970e 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1430,7 +1430,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
vlan_offset = offsetof(struct vlan_ethhdr, h_vlan_proto);
- ret = skb_copy_datagram_iter(skb, 0, iter, vlan_offset);
+ ret = __skb_copy_datagram_iter(skb, 0, iter, vlan_offset);
if (ret || !iov_iter_count(iter))
goto done;
@@ -1439,7 +1439,8 @@ static ssize_t tun_put_user(struct tun_struct *tun,
goto done;
}
- skb_copy_datagram_iter(skb, vlan_offset, iter, skb->len - vlan_offset);
+ /* XXX: no error check? */
+ __skb_copy_datagram_iter(skb, vlan_offset, iter, skb->len -
vlan_offset);
done:
/* caller is in process context, */
@@ -1501,6 +1502,7 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct
tun_file *tfile,
{
struct sk_buff *skb;
ssize_t ret;
+ struct iov_iter saved;
int err;
tun_debug(KERN_INFO, tun, "tun_do_read\n");
@@ -1513,11 +1515,14 @@ static ssize_t tun_do_read(struct tun_struct *tun,
struct tun_file *tfile,
if (!skb)
return err;
+ saved = *to;
ret = tun_put_user(tun, tfile, skb, to);
- if (unlikely(ret < 0))
+ if (unlikely(ret < 0)) {
+ *to = saved;
kfree_skb(skb);
- else
+ } else {
consume_skb(skb);
+ }
return ret;
}
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f1adddc1c5ac..ee8d962373af 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3060,8 +3060,17 @@ struct sk_buff *skb_recv_datagram(struct sock *sk,
unsigned flags, int noblock,
int *err);
unsigned int datagram_poll(struct file *file, struct socket *sock,
struct poll_table_struct *wait);
-int skb_copy_datagram_iter(const struct sk_buff *from, int offset,
+int __skb_copy_datagram_iter(const struct sk_buff *from, int offset,
struct iov_iter *to, int size);
+static inline int skb_copy_datagram_iter(const struct sk_buff *from, int
offset,
+ struct iov_iter *to, int size)
+{
+ struct iov_iter saved = *to;
+ int res = __skb_copy_datagram_iter(from, offset, to, size);
+ if (unlikely(res))
+ *to = saved;
+ return res;
+}
static inline int skb_copy_datagram_msg(const struct sk_buff *from, int offset,
struct msghdr *msg, int size)
{
diff --git a/net/core/datagram.c b/net/core/datagram.c
index ea633342ab0d..33ff2046dda1 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -394,7 +394,7 @@ EXPORT_SYMBOL(skb_kill_datagram);
* @to: iovec iterator to copy to
* @len: amount of data to copy from buffer to iovec
*/
-int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
+int __skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
struct iov_iter *to, int len)
{
int start = skb_headlen(skb);
@@ -445,7 +445,7 @@ int skb_copy_datagram_iter(const struct sk_buff *skb, int
offset,
if ((copy = end - offset) > 0) {
if (copy > len)
copy = len;
- if (skb_copy_datagram_iter(frag_iter, offset - start,
+ if (__skb_copy_datagram_iter(frag_iter, offset - start,
to, copy))
goto fault;
if ((len -= copy) == 0)
@@ -471,7 +471,7 @@ int skb_copy_datagram_iter(const struct sk_buff *skb, int
offset,
return 0;
}
-EXPORT_SYMBOL(skb_copy_datagram_iter);
+EXPORT_SYMBOL(__skb_copy_datagram_iter);
/**
* skb_copy_datagram_from_iter - Copy a datagram from an iov_iter.
@@ -750,14 +750,16 @@ int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
{
__wsum csum;
int chunk = skb->len - hlen;
+ struct iov_iter saved;
if (!chunk)
return 0;
+ saved = msg->msg_iter;
if (msg_data_left(msg) < chunk) {
if (__skb_checksum_complete(skb))
goto csum_error;
- if (skb_copy_datagram_msg(skb, hlen, msg, chunk))
+ if (__skb_copy_datagram_iter(skb, hlen, &msg->msg_iter, chunk))
goto fault;
} else {
csum = csum_partial(skb->data, hlen, skb->csum);
@@ -771,8 +773,10 @@ int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
}
return 0;
csum_error:
+ msg->msg_iter = saved;
return -EINVAL;
fault:
+ msg->msg_iter = saved;
return -EFAULT;
}
EXPORT_SYMBOL(skb_copy_and_csum_datagram_msg);
