From: Thomas Graf Date: Thu, 18 Dec 2014 10:30:26 +0000 (+0000) Subject: netlink: Don't reorder loads/stores before marking mmap netlink frame as available X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=a18e6a186f53af06937a2c268c72443336f4ab56;p=openwrt%2Fstaging%2Fblogic.git netlink: Don't reorder loads/stores before marking mmap netlink frame as available Each mmap Netlink frame contains a status field which indicates whether the frame is unused, reserved, contains data or needs to be skipped. Both loads and stores may not be reordeded and must complete before the status field is changed and another CPU might pick up the frame for use. Use an smp_mb() to cover needs of both types of callers to netlink_set_status(), callers which have been reading data frame from the frame, and callers which have been filling or releasing and thus writing to the frame. - Example code path requiring a smp_rmb(): memcpy(skb->data, (void *)hdr + NL_MMAP_HDRLEN, hdr->nm_len); netlink_set_status(hdr, NL_MMAP_STATUS_UNUSED); - Example code path requiring a smp_wmb(): hdr->nm_uid = from_kuid(sk_user_ns(sk), NETLINK_CB(skb).creds.uid); hdr->nm_gid = from_kgid(sk_user_ns(sk), NETLINK_CB(skb).creds.gid); netlink_frame_flush_dcache(hdr); netlink_set_status(hdr, NL_MMAP_STATUS_VALID); Fixes: f9c228 ("netlink: implement memory mapped recvmsg()") Reported-by: Eric Dumazet Signed-off-by: Thomas Graf Signed-off-by: David S. Miller --- diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index a64680a3e782..074cf3e91c6f 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -550,9 +550,9 @@ static enum nl_mmap_status netlink_get_status(const struct nl_mmap_hdr *hdr) static void netlink_set_status(struct nl_mmap_hdr *hdr, enum nl_mmap_status status) { + smp_mb(); hdr->nm_status = status; flush_dcache_page(pgvec_to_page(hdr)); - smp_wmb(); } static struct nl_mmap_hdr *