net: Block MSG_SENDPAGE_* from being passed to sendmsg() by userspace

It is necessary to allow MSG_SENDPAGE_* to be passed into ->sendmsg() to
allow sendmsg(MSG_SPLICE_PAGES) to replace ->sendpage().  Unblocking them
in the network protocol, however, allows these flags to be passed in by
userspace too[1].

Fix this by marking MSG_SENDPAGE_NOPOLICY, MSG_SENDPAGE_NOTLAST and
MSG_SENDPAGE_DECRYPTED as internal flags, which causes sendmsg() to object
if they are passed to sendmsg() by userspace.  Network protocol ->sendmsg()
implementations can then allow them through.

Note that it should be possible to remove MSG_SENDPAGE_NOTLAST once
sendpage is removed as a whole slew of pages will be passed in in one go by
splice through sendmsg, with MSG_MORE being set if it has more data waiting
in the pipe.

Signed-off-by: David Howells <[email protected]>
cc: Chuck Lever <[email protected]>
cc: Boris Pismenny <[email protected]>
cc: John Fastabend <[email protected]>
cc: Jens Axboe <[email protected]>
cc: Matthew Wilcox <[email protected]>
Link: https://lore.kernel.org/r/[email protected]/ [1]
Signed-off-by: Jakub Kicinski <[email protected]>

0 files changed, 0 insertions, 0 deletions