On Tue, Nov 26, 2024 at 5:45 AM Christian Göttsche
<cgoettsche@xxxxxxxxxxxxx> wrote:
>
> 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>
For these three patches:
Acked-by: James Carter <jwcart2@xxxxxxxxx>
> ---
> 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
>
>
