libbpf: Fix potential NULL pointer dereference

commit afd0be7299533bb2e2b09104399d8a467ecbd2c5 upstream.

Wait until after the UMEM is checked for null to dereference it.

Fixes: 43f1bc1efff1 ("libbpf: Restore umem state after socket create failure")
Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210408052009.7844-1-ciara.loftus@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 5f7b85f..7150e34 100644 (file)
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -703,18 +703,19 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
                              struct xsk_ring_cons *comp,
                              const struct xsk_socket_config *usr_config)
 {
+       bool unmap, rx_setup_done = false, tx_setup_done = false;
        void *rx_map = NULL, *tx_map = NULL;
        struct sockaddr_xdp sxdp = {};
        struct xdp_mmap_offsets off;
        struct xsk_socket *xsk;
        struct xsk_ctx *ctx;
        int err, ifindex;
-       bool unmap = umem->fill_save != fill;
-       bool rx_setup_done = false, tx_setup_done = false;
 
        if (!umem || !xsk_ptr || !(rx || tx))
                return -EFAULT;
 
+       unmap = umem->fill_save != fill;
+
        xsk = calloc(1, sizeof(*xsk));
        if (!xsk)
                return -ENOMEM;