libbpf: Fix null dereference in xsk_socket__delete

Fix a possible null pointer dereference in xsk_socket__delete that
will occur if a null pointer is fed into the function.

Fixes: 3c545a59a8a2 ("libbpf: Support shared umems between queues and devices")
Reported-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1604396490-12129-2-git-send-email-magnus.karlsson@gmail.com

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index e3c98c007825cf10c8fd4b08452d720166d15bb0..504b7a85d4456760a83302de97d3c98ff5e80d76 100644 (file)
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -891,13 +891,14 @@ int xsk_umem__delete(struct xsk_umem *umem)
 void xsk_socket__delete(struct xsk_socket *xsk)
 {
        size_t desc_sz = sizeof(struct xdp_desc);
-       struct xsk_ctx *ctx = xsk->ctx;
        struct xdp_mmap_offsets off;
+       struct xsk_ctx *ctx;
        int err;
 
        if (!xsk)
                return;
 
+       ctx = xsk->ctx;
        if (ctx->prog_fd != -1) {
                xsk_delete_bpf_maps(xsk);
                close(ctx->prog_fd);