libbpf: Clear map_info before each bpf_obj_get_info_by_fd

BugLink: https://bugs.launchpad.net/bugs/1919492
commit 2b2aedabc44e9660f90ccf7ba1ca2706d75f411f upstream.

xsk_lookup_bpf_maps, based on prog_fd, looks whether current prog has a
reference to XSKMAP. BPF prog can include insns that work on various BPF
maps and this is covered by iterating through map_ids.

The bpf_map_info that is passed to bpf_obj_get_info_by_fd for filling
needs to be cleared at each iteration, so that it doesn't contain any
outdated fields and that is currently missing in the function of
interest.

To fix that, zero-init map_info via memset before each
bpf_obj_get_info_by_fd call.

Also, since the area of this code is touched, in general strcmp is
considered harmful, so let's convert it to strncmp and provide the
size of the array name for current map_info.

While at it, do s/continue/break/ once we have found the xsks_map to
terminate the search.

Fixes: 5750902a6e9b ("libbpf: proper XSKMAP cleanup")
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Link: https://lore.kernel.org/bpf/20210303185636.18070-4-maciej.fijalkowski@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index e3e41ceeb1bc63991a6376f2882cb02683b74379..06746d96742f3774693787d3e394f84c10c4215e 100644 (file)
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -535,15 +535,16 @@ static int xsk_lookup_bpf_maps(struct xsk_socket *xsk)
                if (fd < 0)
                        continue;
 
+               memset(&map_info, 0, map_len);
                err = bpf_obj_get_info_by_fd(fd, &map_info, &map_len);
                if (err) {
                        close(fd);
                        continue;
                }
 
-               if (!strcmp(map_info.name, "xsks_map")) {
+               if (!strncmp(map_info.name, "xsks_map", sizeof(map_info.name))) {
                        ctx->xsks_map_fd = fd;
-                       continue;
+                       break;
                }
 
                close(fd);