[bpf,3/3] libbpf: clear map_info before each bpf_obj_get_info_by_fd

Commit Message

Maciej Fijalkowski March 3, 2021, 3:51 p.m. UTC

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outdated fields and that is currently missing in the function of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
length of the array name from current map_info.

Last but not least, 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 <[e-mail]>
---
 tools/lib/bpf/xsk.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Patch

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index ffbb588724d8..e56b2d76efc2 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -610,15 +610,16 @@  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", strlen(map_info.name))) {
 			ctx->xsks_map_fd = fd;
-			continue;
+			break;
 		}
 
 		close(fd);