libbpf: Do not require executable permission for shared libraries

Currently, resolve_full_path() requires executable permission for both
programs and shared libraries. This causes failures on distos like Debian
since the shared libraries are not installed executable and Linux is not
requiring shared libraries to have executable permissions. Let's remove
executable permission check for shared libraries.

Reported-by: Goro Fuji <goro@fastly.com>
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220806102021.3867130-1-hengqi.chen@gmail.com

tools/lib/bpf/libbpf.c

@@ -10664,15 +10664,17 @@ static const char *arch_specific_lib_paths(void)
 static int resolve_full_path(const char *file, char *result, size_t result_sz)
 {
 	const char *search_paths[3] = {};
-	int i;
+	int i, perm;
 
 	if (str_has_sfx(file, ".so") || strstr(file, ".so.")) {
 		search_paths[0] = getenv("LD_LIBRARY_PATH");
 		search_paths[1] = "/usr/lib64:/usr/lib";
 		search_paths[2] = arch_specific_lib_paths();
+		perm = R_OK;
 	} else {
 		search_paths[0] = getenv("PATH");
 		search_paths[1] = "/usr/bin:/usr/sbin";
+		perm = R_OK | X_OK;
 	}
 
 	for (i = 0; i < ARRAY_SIZE(search_paths); i++) {
@@ -10691,8 +10693,8 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
 			if (!seg_len)
 				continue;
 			snprintf(result, result_sz, "%.*s/%s", seg_len, s, file);
-			/* ensure it is an executable file/link */
-			if (access(result, R_OK | X_OK) < 0)
+			/* ensure it has required permissions */
+			if (access(result, perm) < 0)
 				continue;
 			pr_debug("resolved '%s' to '%s'\n", file, result);
 			return 0;