Commit a18e6a18 authored by Thomas Graf's avatar Thomas Graf Committed by David S. Miller

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: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarThomas Graf <tgraf@suug.ch>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4682a035
...@@ -550,9 +550,9 @@ static enum nl_mmap_status netlink_get_status(const struct nl_mmap_hdr *hdr) ...@@ -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, static void netlink_set_status(struct nl_mmap_hdr *hdr,
enum nl_mmap_status status) enum nl_mmap_status status)
{ {
smp_mb();
hdr->nm_status = status; hdr->nm_status = status;
flush_dcache_page(pgvec_to_page(hdr)); flush_dcache_page(pgvec_to_page(hdr));
smp_wmb();
} }
static struct nl_mmap_hdr * static struct nl_mmap_hdr *
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment