From: Christian Göttsche <cgzones@xxxxxxxxxxxxxx>
Remove a memory allocation during a common file label lookup,
e.g. requested by restorecon(8)/setfiles(8), by using a local stack
buffer for a potential lookup result.
Additional minor optimization tweaks.
Signed-off-by: Christian Göttsche <cgzones@xxxxxxxxxxxxxx>
---
v2: drop claim about this being the sole memory allocation, since
applying a substitution path allocates as well
---
libselinux/src/label_file.c | 103 +++++++++++++++++-------------
libselinux/src/selinux_internal.h | 8 +++
2 files changed, 68 insertions(+), 43 deletions(-)
diff --git a/libselinux/src/label_file.c b/libselinux/src/label_file.c
index 189a5ed2..4e212aa4 100644
--- a/libselinux/src/label_file.c
+++ b/libselinux/src/label_file.c
@@ -1467,12 +1467,30 @@ FUZZ_EXTERN void free_lookup_result(struct lookup_result *result)
}
}
-static struct lookup_result *lookup_check_node(struct spec_node *node, const char *key, uint8_t file_kind, bool partial, bool find_all)
+/**
+ * lookup_check_node() - Try to find a file context definition in the given node or parents.
+ * @node: The deepest specification node to match against. Parent nodes are successively
+ * searched on no match or when finding all matches.
+ * @key: The absolute file path to look up.
+ * @file_kind: The kind of the file to look up (translated from file type into LABEL_FILE_KIND_*).
+ * @partial: Whether to partially match the given file path or completely.
+ * @find_all: Whether to find all file context definitions or just the most specific.
+ * @buf: A pre-allocated buffer for a potential result to avoid allocating it on the heap or
+ * NULL. Mututal exclusive with @find_all.
+ *
+ * Return: A pointer to a file context definition if a match was found. If @find_all was specified
+ * its a linked list of all results. If @buf was specified it is returned on a match found.
+ * NULL is returned in case of no match found.
+ */
+static struct lookup_result *lookup_check_node(struct spec_node *node, const char *key, uint8_t file_kind,
+ bool partial, bool find_all, struct lookup_result *buf)
{
struct lookup_result *result = NULL;
struct lookup_result **next = &result;
size_t key_len = strlen(key);
+ assert(!(find_all && buf != NULL));
+
for (struct spec_node *n = node; n; n = n->parent) {
uint32_t literal_idx = search_literal_spec(n->literal_specs, n->literal_specs_num, key, key_len, partial);
@@ -1495,10 +1513,14 @@ static struct lookup_result *lookup_check_node(struct spec_node *node, const cha
return NULL;
}
- r = malloc(sizeof(*r));
- if (!r) {
- free_lookup_result(result);
- return NULL;
+ if (likely(buf)) {
+ r = buf;
+ } else {
+ r = malloc(sizeof(*r));
+ if (!r) {
+ free_lookup_result(result);
+ return NULL;
+ }
}
*r = (struct lookup_result) {
@@ -1510,11 +1532,11 @@ static struct lookup_result *lookup_check_node(struct spec_node *node, const cha
.next = NULL,
};
+ if (likely(!find_all))
+ return r;
+
*next = r;
next = &r->next;
-
- if (!find_all)
- return result;
}
literal_idx++;
@@ -1556,10 +1578,14 @@ static struct lookup_result *lookup_check_node(struct spec_node *node, const cha
return NULL;
}
- r = malloc(sizeof(*r));
- if (!r) {
- free_lookup_result(result);
- return NULL;
+ if (likely(buf)) {
+ r = buf;
+ } else {
+ r = malloc(sizeof(*r));
+ if (!r) {
+ free_lookup_result(result);
+ return NULL;
+ }
}
*r = (struct lookup_result) {
@@ -1571,12 +1597,12 @@ static struct lookup_result *lookup_check_node(struct spec_node *node, const cha
.next = NULL,
};
+ if (likely(!find_all))
+ return r;
+
*next = r;
next = &r->next;
- if (!find_all)
- return result;
-
continue;
}
@@ -1692,7 +1718,8 @@ FUZZ_EXTERN struct lookup_result *lookup_all(struct selabel_handle *rec,
const char *key,
int type,
bool partial,
- bool find_all)
+ bool find_all,
+ struct lookup_result *buf)
{
struct saved_data *data = (struct saved_data *)rec->data;
struct lookup_result *result = NULL;
@@ -1704,18 +1731,18 @@ FUZZ_EXTERN struct lookup_result *lookup_all(struct selabel_handle *rec,
unsigned int sofar = 0;
char *sub = NULL;
- if (!key) {
+ if (unlikely(!key)) {
errno = EINVAL;
goto finish;
}
- if (!data->num_specs) {
+ if (unlikely(!data->num_specs)) {
errno = ENOENT;
goto finish;
}
/* Remove duplicate slashes */
- if ((next_slash = strstr(key, "//"))) {
+ if (unlikely(next_slash = strstr(key, "//"))) {
clean_key = (char *) malloc(strlen(key) + 1);
if (!clean_key)
goto finish;
@@ -1732,12 +1759,12 @@ FUZZ_EXTERN struct lookup_result *lookup_all(struct selabel_handle *rec,
/* remove trailing slash */
len = strlen(key);
- if (len == 0) {
+ if (unlikely(len == 0)) {
errno = EINVAL;
goto finish;
}
- if (len > 1 && key[len - 1] == '/') {
+ if (unlikely(len > 1 && key[len - 1] == '/')) {
/* reuse clean_key from above if available */
if (!clean_key) {
clean_key = (char *) malloc(len);
@@ -1757,7 +1784,7 @@ FUZZ_EXTERN struct lookup_result *lookup_all(struct selabel_handle *rec,
node = lookup_find_deepest_node(data->root, key);
- result = lookup_check_node(node, key, file_kind, partial, find_all);
+ result = lookup_check_node(node, key, file_kind, partial, find_all, buf);
finish:
free(clean_key);
@@ -1768,14 +1795,9 @@ finish:
static struct lookup_result *lookup_common(struct selabel_handle *rec,
const char *key,
int type,
- bool partial) {
- struct lookup_result *result = lookup_all(rec, key, type, partial, false);
- if (!result)
- return NULL;
-
- free_lookup_result(result->next);
- result->next = NULL;
- return result;
+ bool partial,
+ struct lookup_result *buf) {
+ return lookup_all(rec, key, type, partial, false, buf);
}
/*
@@ -1835,7 +1857,7 @@ static bool hash_all_partial_matches(struct selabel_handle *rec, const char *key
{
assert(digest);
- struct lookup_result *matches = lookup_all(rec, key, 0, true, true);
+ struct lookup_result *matches = lookup_all(rec, key, 0, true, true, NULL);
if (!matches) {
return false;
}
@@ -1864,25 +1886,20 @@ static bool hash_all_partial_matches(struct selabel_handle *rec, const char *key
static struct selabel_lookup_rec *lookup(struct selabel_handle *rec,
const char *key, int type)
{
- struct lookup_result *result;
- struct selabel_lookup_rec *lookup_result;
+ struct lookup_result buf, *result;
- result = lookup_common(rec, key, type, false);
+ result = lookup_common(rec, key, type, false, &buf);
if (!result)
return NULL;
- lookup_result = result->lr;
- free_lookup_result(result);
- return lookup_result;
+ return result->lr;
}
static bool partial_match(struct selabel_handle *rec, const char *key)
{
- struct lookup_result *result = lookup_common(rec, key, 0, true);
- bool ret = result;
+ struct lookup_result buf;
- free_lookup_result(result);
- return ret;
+ return !!lookup_common(rec, key, 0, true, &buf);
}
static struct selabel_lookup_rec *lookup_best_match(struct selabel_handle *rec,
@@ -1904,7 +1921,7 @@ static struct selabel_lookup_rec *lookup_best_match(struct selabel_handle *rec,
results = calloc(n+1, sizeof(*results));
if (!results)
return NULL;
- results[0] = lookup_common(rec, key, type, false);
+ results[0] = lookup_common(rec, key, type, false, NULL);
if (results[0]) {
if (!results[0]->has_meta_chars) {
/* exact match on key */
@@ -1915,7 +1932,7 @@ static struct selabel_lookup_rec *lookup_best_match(struct selabel_handle *rec,
prefix_len = results[0]->prefix_len;
}
for (i = 1; i <= n; i++) {
- results[i] = lookup_common(rec, aliases[i-1], type, false);
+ results[i] = lookup_common(rec, aliases[i-1], type, false, NULL);
if (results[i]) {
if (!results[i]->has_meta_chars) {
/* exact match on alias */
diff --git a/libselinux/src/selinux_internal.h b/libselinux/src/selinux_internal.h
index 372837dd..964b8418 100644
--- a/libselinux/src/selinux_internal.h
+++ b/libselinux/src/selinux_internal.h
@@ -142,4 +142,12 @@ static inline void fclose_errno_safe(FILE *stream)
errno = saved_errno;
}
+#ifdef __GNUC__
+# define likely(x) __builtin_expect(!!(x), 1)
+# define unlikely(x) __builtin_expect(!!(x), 0)
+#else
+# define likely(x) (x)
+# define unlikely(x) (x)
+#endif /* __GNUC__ */
+
#endif /* SELINUX_INTERNAL_H_ */
--
2.45.2
