libbpf: Fix compatibility problem in xsk_socket__create

Fix a compatibility problem when the old XDP_SHARED_UMEM mode is used
together with the xsk_socket__create() call. In the old XDP_SHARED_UMEM
mode, only sharing of the same device and queue id was allowed, and
in this mode, the fill ring and completion ring were shared between
the AF_XDP sockets.

Therefore, it was perfectly fine to call the xsk_socket__create() API
for each socket and not use the new xsk_socket__create_shared() API.
This behavior was ruined by the commit introducing XDP_SHARED_UMEM
support between different devices and/or queue ids. This patch restores
the ability to use xsk_socket__create in these circumstances so that
backward compatibility is not broken.

Fixes: 2f6324a3937f ("libbpf: Support shared umems between queues and devices")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/1602070946-11154-1-git-send-email-magnus.karlsson@gmail.com

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 30b4ca5d2ac7e08d888ac216128fdf06c0dfeefd..e3c98c007825cf10c8fd4b08452d720166d15bb0 100644 (file)
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -705,7 +705,7 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
        struct xsk_ctx *ctx;
        int err, ifindex;
 
-       if (!umem || !xsk_ptr || !(rx || tx) || !fill || !comp)
+       if (!umem || !xsk_ptr || !(rx || tx))
                return -EFAULT;
 
        xsk = calloc(1, sizeof(*xsk));
@@ -735,6 +735,11 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 
        ctx = xsk_get_ctx(umem, ifindex, queue_id);
        if (!ctx) {
+               if (!fill || !comp) {
+                       err = -EFAULT;
+                       goto out_socket;
+               }
+
                ctx = xsk_create_ctx(xsk, umem, ifindex, ifname, queue_id,
                                     fill, comp);
                if (!ctx) {