[PATCH nft,v2] mnl: do not cache sender buffer size

[PATCH nft,v2] mnl: do not cache sender buffer size

[Pablo Neira Ayuso]

SO_SNDBUF never fails, this socket option just provides a hint to the
kernel.  SO_SNDBUFFORCE sets the buffer size to zero if the value goes
over INT_MAX. Userspace is caching the buffer hint that sends to the
kernel, so it might leave userspace out of sync if the kernel ignores
the hint. Do not make assumptions, fetch the sender buffer size from the
kernel via getsockopt().

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
v2: Missing len variable initialization - Florian Westphal.

 src/mnl.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/mnl.c b/src/mnl.c
index 57ff89f50e23..14fa4a7186fd 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -218,24 +218,24 @@ void mnl_err_list_free(struct mnl_err *err)
 	xfree(err);
 }
 
-static int nlbuffsiz;
-
 static void mnl_set_sndbuffer(const struct mnl_socket *nl,
 			      struct nftnl_batch *batch)
 {
+	socklen_t len = sizeof(int);
+	int sndnlbuffsiz = 0;
 	int newbuffsiz;
 
-	if (nftnl_batch_iovec_len(batch) * BATCH_PAGE_SIZE <= nlbuffsiz)
-		return;
+	getsockopt(mnl_socket_get_fd(nl), SOL_SOCKET, SO_SNDBUF,
+		   &sndnlbuffsiz, &len);
 
 	newbuffsiz = nftnl_batch_iovec_len(batch) * BATCH_PAGE_SIZE;
+	if (newbuffsiz <= sndnlbuffsiz)
+		return;
 
 	/* Rise sender buffer length to avoid hitting -EMSGSIZE */
 	if (setsockopt(mnl_socket_get_fd(nl), SOL_SOCKET, SO_SNDBUFFORCE,
 		       &newbuffsiz, sizeof(socklen_t)) < 0)
 		return;
-
-	nlbuffsiz = newbuffsiz;
 }
 
 static unsigned int nlsndbufsiz;
-- 
2.11.0