From 5844f389429f26a0a62a65561fa3006feaaf6f3b Mon Sep 17 00:00:00 2001
From: Ondrej Mosnacek <omosnace@redhat.com>
Date: Tue, 26 Oct 2021 13:52:32 +0200
Subject: [PATCH] label_file: fix a data race

The 'matches' member of 'struct spec' may be written to by different
threads, so it needs to be accessed using the proper atomic constructs.
Since the actual count of matches doesn't matter and is not used,
convert this field to a bool and just atomically set/read it using GCC
__atomic builtins (which are already being used in another place).

If the compiler lacks support for __atomic builtins (which seem to have
been introduced in GCC 4.1), just fail the compilation. I don't think
it's worth tryin to invent a workaround to support a 15 years old
compiler.

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
---
 libselinux/src/label_file.c | 15 +++++++++++++--
 libselinux/src/label_file.h |  2 +-
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/libselinux/src/label_file.c b/libselinux/src/label_file.c
index c1306c9979e7..33d395e414f0 100644
--- a/libselinux/src/label_file.c
+++ b/libselinux/src/label_file.c
@@ -951,7 +951,12 @@ static struct spec **lookup_all(struct selabel_handle *rec,
 			rc = regex_match(spec->regex, key, partial);
 			if (rc == REGEX_MATCH || (partial && rc == REGEX_MATCH_PARTIAL)) {
 				if (rc == REGEX_MATCH) {
-					spec->matches++;
+#ifdef __ATOMIC_RELAXED
+					__atomic_store_n(&spec->any_matches,
+							 true, __ATOMIC_RELAXED);
+#else
+#error "Please use a compiler that supports __atomic builtins"
+#endif
 				}
 
 				if (strcmp(spec_arr[i].lr.ctx_raw, "<<none>>") == 0) {
@@ -1249,9 +1254,15 @@ static void stats(struct selabel_handle *rec)
 	struct saved_data *data = (struct saved_data *)rec->data;
 	unsigned int i, nspec = data->nspec;
 	struct spec *spec_arr = data->spec_arr;
+	bool any_matches;
 
 	for (i = 0; i < nspec; i++) {
-		if (spec_arr[i].matches == 0) {
+#ifdef __ATOMIC_RELAXED
+		any_matches = __atomic_load_n(&spec_arr[i].any_matches, __ATOMIC_RELAXED);
+#else
+#error "Please use a compiler that supports __atomic builtins"
+#endif
+		if (!any_matches) {
 			if (spec_arr[i].type_str) {
 				COMPAT_LOG(SELINUX_WARNING,
 				    "Warning!  No matches for (%s, %s, %s)\n",
diff --git a/libselinux/src/label_file.h b/libselinux/src/label_file.h
index 343ffc705e43..b453e13f8075 100644
--- a/libselinux/src/label_file.h
+++ b/libselinux/src/label_file.h
@@ -51,7 +51,7 @@ struct spec {
 	bool regex_compiled; /* bool to indicate if the regex is compiled */
 	pthread_mutex_t regex_lock; /* lock for lazy compilation of regex */
 	mode_t mode;		/* mode format value */
-	int matches;		/* number of matching pathnames */
+	bool any_matches;	/* did any pathname match? */
 	int stem_id;		/* indicates which stem-compression item */
 	char hasMetaChars;	/* regular expression has meta-chars */
 	char from_mmap;		/* this spec is from an mmap of the data */
-- 
2.33.1