[PATCH 4.4 17/18] ipv6: use READ_ONCE() for inet->hdrincl as in ipv4

Greg Kroah-Hartman
2020-05-04T18:15:47Z

From: Olivier Matz <olivier.matz@6wind.com>

commit 59e3e4b52663a9d97efbce7307f62e4bc5c9ce91 upstream.

As it was done in commit 8f659a03a0ba ("net: ipv4: fix for a race
condition in raw_sendmsg") and commit 20b50d79974e ("net: ipv4: emulate
READ_ONCE() on ->hdrincl bit-field in raw_sendmsg()") for ipv4, copy the
value of inet->hdrincl in a local variable, to avoid introducing a race
condition in the next commit.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/ipv6/raw.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -757,6 +757,7 @@ static int rawv6_sendmsg(struct sock *sk
int hlimit = -1;
int tclass = -1;
int dontfrag = -1;
+ int hdrincl;
u16 proto;
int err;

@@ -770,6 +771,13 @@ static int rawv6_sendmsg(struct sock *sk
if (msg->msg_flags & MSG_OOB)
return -EOPNOTSUPP;

+ /* hdrincl should be READ_ONCE(inet->hdrincl)
+ * but READ_ONCE() doesn't work with bit fields.
+ * Doing this indirectly yields the same result.
+ */
+ hdrincl = inet->hdrincl;
+ hdrincl = READ_ONCE(hdrincl);
+
/*
* Get and verify the address.
*/
@@ -878,7 +886,7 @@ static int rawv6_sendmsg(struct sock *sk
fl6.flowi6_oif = np->ucast_oif;
security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));

- if (inet->hdrincl)
+ if (hdrincl)
fl6.flowi6_flags |= FLOWI_FLAG_KNOWN_NH;

dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
@@ -899,7 +907,7 @@ static int rawv6_sendmsg(struct sock *sk
goto do_confirm;

back_from_confirm:
- if (inet->hdrincl)
+ if (hdrincl)
err = rawv6_send_hdrinc(sk, msg, len, &fl6, &dst, msg->msg_flags);
else {
lock_sock(sk);