[apparmor] [PATCH 4/6] libapparmor: Migrate aa_features API to openat() style

[Tyler Hicks]

Instead of only accepting a path in the aa_features API, accept a
directory file descriptor and a path like then openat() family of
syscalls. This type of interface is better since it can operate exactly
like a path-only interface, by passing AT_FDCWD or -1 as the dirfd.
However, using the dirfd/path combination, it can eliminate string
allocations needed to open files in subdirectories along with the
even more important benefits mentioned in the open(2) man page.

Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
---
 libraries/libapparmor/include/sys/apparmor.h |  5 +++--
 libraries/libapparmor/src/features.c         | 20 ++++++++++++--------
 libraries/libapparmor/src/policy_cache.c     |  4 ++--
 parser/parser_main.c                         |  2 +-
 4 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/libraries/libapparmor/include/sys/apparmor.h b/libraries/libapparmor/include/sys/apparmor.h
index 43d6efc..2643cde 100644
--- a/libraries/libapparmor/include/sys/apparmor.h
+++ b/libraries/libapparmor/include/sys/apparmor.h
@@ -105,14 +105,15 @@ extern int aa_query_label(uint32_t mask, char *query, size_t size, int *allow,
 	(aa_change_hat_vargs)(T, __macroarg_counter(X), X)
 
 typedef struct aa_features aa_features;
-int aa_features_new(aa_features **features, const char *path);
+int aa_features_new(aa_features **features, int dirfd, const char *path);
 int aa_features_new_from_string(aa_features **features,
 				const char *string, size_t size);
 int aa_features_new_from_kernel(aa_features **features);
 aa_features *aa_features_ref(aa_features *features);
 void aa_features_unref(aa_features *features);
 
-int aa_features_write_to_file(aa_features *features, const char *path);
+int aa_features_write_to_file(aa_features *features,
+			      int dirfd, const char *path);
 bool aa_features_is_equal(aa_features *features1, aa_features *features2);
 bool aa_features_supports(aa_features *features, const char *str);
 
diff --git a/libraries/libapparmor/src/features.c b/libraries/libapparmor/src/features.c
index 0bb90ee..12a708b 100644
--- a/libraries/libapparmor/src/features.c
+++ b/libraries/libapparmor/src/features.c
@@ -359,12 +359,13 @@ static bool walk_one(const char **str, const struct component *component,
  * aa_features_new - create a new features based on a path
  * @features: will point to the address of an allocated and initialized
  *            aa_features object upon success
+ * @dirfd: directory file descriptor or AT_FDCWD (see openat(2))
  * @path: path to a features file or directory
  *
  * Returns: 0 on success, -1 on error with errno set and *@features pointing to
  *          NULL
  */
-int aa_features_new(aa_features **features, const char *path)
+int aa_features_new(aa_features **features, int dirfd, const char *path)
 {
 	struct stat stat_file;
 	aa_features *f;
@@ -372,7 +373,7 @@ int aa_features_new(aa_features **features, const char *path)
 
 	*features = NULL;
 
-	if (stat(path, &stat_file) == -1)
+	if (fstatat(dirfd, path, &stat_file, 0) == -1)
 		return -1;
 
 	f = calloc(1, sizeof(*f));
@@ -383,8 +384,8 @@ int aa_features_new(aa_features **features, const char *path)
 	aa_features_ref(f);
 
 	retval = S_ISDIR(stat_file.st_mode) ?
-		 load_features_dir(AT_FDCWD, path, f->string, STRING_SIZE) :
-		 load_features_file(AT_FDCWD, path, f->string, STRING_SIZE);
+		 load_features_dir(dirfd, path, f->string, STRING_SIZE) :
+		 load_features_file(dirfd, path, f->string, STRING_SIZE);
 	if (retval == -1) {
 		int save = errno;
 
@@ -443,7 +444,7 @@ int aa_features_new_from_string(aa_features **features,
  */
 int aa_features_new_from_kernel(aa_features **features)
 {
-	return aa_features_new(features, FEATURES_FILE);
+	return aa_features_new(features, -1, FEATURES_FILE);
 }
 
 /**
@@ -471,19 +472,22 @@ void aa_features_unref(aa_features *features)
 /**
  * aa_features_write_to_file - write a string representation to a file
  * @features: the features
+ * @dirfd: directory file descriptor or AT_FDCWD (see openat(2))
  * @path: the path to write to
  *
  * Returns: 0 on success, -1 on error with errno set
  */
-int aa_features_write_to_file(aa_features *features, const char *path)
+int aa_features_write_to_file(aa_features *features,
+			      int dirfd, const char *path)
 {
 	autoclose int fd = -1;
 	size_t size;
 	ssize_t retval;
 	char *string;
 
-	fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_SYNC | O_CLOEXEC,
-		  S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+	fd = openat(dirfd, path,
+		    O_WRONLY | O_CREAT | O_TRUNC | O_SYNC | O_CLOEXEC,
+		    S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
 	if (fd == -1)
 		return -1;
 
diff --git a/libraries/libapparmor/src/policy_cache.c b/libraries/libapparmor/src/policy_cache.c
index 22f84dd..515e2d0 100644
--- a/libraries/libapparmor/src/policy_cache.c
+++ b/libraries/libapparmor/src/policy_cache.c
@@ -56,7 +56,7 @@ static int create_cache(aa_policy_cache *policy_cache, aa_features *features)
 		goto error;
 
 create_file:
-	if (aa_features_write_to_file(features,
+	if (aa_features_write_to_file(features, -1,
 				      policy_cache->features_path) == -1)
 		goto error;
 
@@ -85,7 +85,7 @@ error:
 static int init_cache_features(aa_policy_cache *policy_cache,
 			       aa_features *kernel_features, bool create)
 {
-	if (aa_features_new(&policy_cache->features,
+	if (aa_features_new(&policy_cache->features, -1,
 			    policy_cache->features_path)) {
 		policy_cache->features = NULL;
 		if (!create || errno != ENOENT)
diff --git a/parser/parser_main.c b/parser/parser_main.c
index 1069e9d..428c3ea 100644
--- a/parser/parser_main.c
+++ b/parser/parser_main.c
@@ -397,7 +397,7 @@ static int process_arg(int c, char *optarg)
 		}
 		break;
 	case 'M':
-		if (aa_features_new(&features, optarg)) {
+		if (aa_features_new(&features, AT_FDCWD, optarg)) {
 			fprintf(stderr,
 				"Failed to load features from '%s': %m\n",
 				optarg);
-- 
2.1.4