libselinux: Add selabel_digest function

selabel_digest(3) if enabled by the SELABEL_OPT_DIGEST option during
selabel_open(3) will return an SHA1 digest of the spec files, plus
a list of the specfiles used to calculate the digest. There is a
test utility supplied that will demonstrate the functionality.

The use case for selabel_digest(3) is to implement an selinux_restorecon
function based on the Android version that writes a hash of the
file_contexts files to an extended attribute to enhance performance
(see external/libselinux/src/android.c selinux_android_restorecon()).

Signed-off-by: Richard Haines <richard_c_haines@btinternet.com>

libselinux/include/selinux/label.h

@@ -49,8 +49,10 @@ struct selabel_handle;
 #define SELABEL_OPT_PATH	3
 /* select a subset of the search space as an optimization (file backend) */
 #define SELABEL_OPT_SUBSET	4
+/* require a hash calculation on spec files */
+#define SELABEL_OPT_DIGEST	5
 /* total number of options */
-#define SELABEL_NOPT		5
+#define SELABEL_NOPT		6
 
 /*
  * Label operations
@@ -106,6 +108,23 @@ int selabel_lookup_best_match(struct selabel_handle *rec, char **con,
 int selabel_lookup_best_match_raw(struct selabel_handle *rec, char **con,
 			      const char *key, const char **aliases, int type);
 
+/**
+ * selabel_digest - Retrieve the SHA1 digest and the list of specfiles used to
+ *		    generate the digest. The SELABEL_OPT_DIGEST option must
+ *		    be set in selabel_open() to initiate the digest generation.
+ * @handle: specifies backend instance to query
+ * @digest: returns a pointer to the SHA1 digest.
+ * @digest_len: returns length of digest in bytes.
+ * @specfiles: a list of specfiles used in the SHA1 digest generation.
+ *	       The list is NULL terminated and will hold @num_specfiles entries.
+ * @num_specfiles: number of specfiles in the list.
+ *
+ * Return %0 on success, -%1 with @errno set on failure.
+ */
+int selabel_digest(struct selabel_handle *rec,
+			    unsigned char **digest, size_t *digest_len,
+			    char ***specfiles, size_t *num_specfiles);
+
 enum selabel_cmp_result {
 	SELABEL_SUBSET,
 	SELABEL_EQUAL,

libselinux/man/man3/selabel_digest.3

@@ -0,0 +1,61 @@
+.TH "selabel_digest" "3" "16 Sept 2015" "" "SELinux API documentation"
+.SH "NAME"
+selabel_digest \- Return digest of specfiles and list of files used
+.
+.SH "SYNOPSIS"
+.B #include <selinux/selinux.h>
+.br
+.B #include <selinux/label.h>
+.sp
+.BI "int selabel_digest(struct selabel_handle *" hnd ,
+.in +\w'int selabel_digest('u
+.BI "unsigned char **" digest ,
+.BI "size_t *" digest_len ,
+.br
+.BI "char ***" specfiles,
+.BI "size_t *" num_specfiles ");"
+.in
+.
+.SH "DESCRIPTION"
+.BR selabel_digest ()
+performs an operation on the handle
+.IR hnd ,
+returning the results of the SHA1 digest pointed to by
+.IR digest ,
+whose length will be
+.IR digest_len .
+The list of specfiles used in the SHA1 digest calculation is returned in
+.I specfiles
+with the number of entries in
+.IR num_specfiles .
+.sp
+To enable
+.BR selabel_digest ()
+to return this information the
+.B SELABEL_OPT_DIGEST
+option must be enable in
+.BR selabel_open (3).
+.sp
+The result of
+.BR selabel_digest ()
+must not be used after
+.BR selabel_close (3).
+.
+.SH "RETURN VALUE"
+On success, zero is returned.  On error, \-1 is returned and
+.I errno
+is set appropriately.
+.
+.SH "ERRORS"
+.TP
+.B EINVAL
+No digest available (returned if
+.B SELABEL_OPT_DIGEST
+option not enabled).
+.TP
+.B ENOMEM
+An attempt to allocate memory failed.
+.
+.SH "SEE ALSO"
+.BR selabel_open (3),
+.BR selinux (8)

libselinux/man/man3/selabel_open.3

@@ -67,6 +67,11 @@ A non-null value for this option enables context validation.  By default,
 is used; a custom validation function can be provided via
 .BR selinux_set_callback (3).
 Note that an invalid context may not be treated as an error unless it is actually encountered during a lookup operation.
+.TP
+.B SELABEL_OPT_DIGEST
+A non-null value for this option enables the generation of an SHA1 digest of
+the spec files loaded as described in
+.BR selabel_digest (3)
 .
 .SH "BACKENDS"
 .TP

libselinux/src/Makefile

@@ -112,7 +112,7 @@ $(LIBA): $(OBJS)
 	$(RANLIB) $@
 
 $(LIBSO): $(LOBJS)
-	$(CC) $(CFLAGS) -shared -o $@ $^ -lpcre -ldl $(LDFLAGS) -L$(LIBDIR) -Wl,-soname,$(LIBSO),-z,defs,-z,relro
+	$(CC) $(CFLAGS) -shared -o $@ $^ -lpcre -ldl -lcrypto $(LDFLAGS) -L$(LIBDIR) -Wl,-soname,$(LIBSO),-z,defs,-z,relro
 	ln -sf $@ $(TARGET) 
 
 $(LIBPC): $(LIBPC).in ../VERSION

libselinux/src/label.c

@@ -10,6 +10,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/stat.h>
 #include <selinux/selinux.h>
 #include "callbacks.h"
 #include "label_internal.h"
@@ -65,15 +66,21 @@ static char *selabel_sub(struct selabel_sub *ptr, const char *src)
 	return NULL;
 }
 
-struct selabel_sub *selabel_subs_init(const char *path, struct selabel_sub *list)
+struct selabel_sub *selabel_subs_init(const char *path,
+					    struct selabel_sub *list,
+					    struct selabel_digest *digest)
 {
 	char buf[1024];
 	FILE *cfg = fopen(path, "r");
-	struct selabel_sub *sub;
+	struct selabel_sub *sub = NULL;
+	struct stat sb;
 
 	if (!cfg)
 		return list;
 
+	if (fstat(fileno(cfg), &sb) < 0)
+		return list;
+
 	while (fgets_unlocked(buf, sizeof(buf) - 1, cfg)) {
 		char *ptr = NULL;
 		char *src = buf;
@@ -115,6 +122,10 @@ struct selabel_sub *selabel_subs_init(const char *path, struct selabel_sub *list
 		sub->next = list;
 		list = sub;
 	}
+
+	if (digest_add_specfile(digest, cfg, NULL, sb.st_size, path) < 0)
+		goto err;
+
 out:
 	fclose(cfg);
 	return list;
@@ -125,6 +136,57 @@ struct selabel_sub *selabel_subs_init(const char *path, struct selabel_sub *list
 	goto out;
 }
 
+static inline struct selabel_digest *selabel_is_digest_set
+				    (const struct selinux_opt *opts,
+				    unsigned n,
+				    struct selabel_digest *entry)
+{
+	struct selabel_digest *digest = NULL;
+
+	while (n--) {
+		if (opts[n].type == SELABEL_OPT_DIGEST &&
+					    opts[n].value == (char *)1) {
+			digest = calloc(1, sizeof(*digest));
+			if (!digest)
+				goto err;
+
+			digest->digest = calloc(1, DIGEST_SPECFILE_SIZE + 1);
+			if (!digest->digest)
+				goto err;
+
+			digest->specfile_list = calloc(DIGEST_FILES_MAX,
+							    sizeof(char *));
+			if (!digest->specfile_list)
+				goto err;
+
+			entry = digest;
+			return entry;
+		}
+	}
+	return NULL;
+
+err:
+	free(digest->digest);
+	free(digest->specfile_list);
+	free(digest);
+	return NULL;
+}
+
+static void selabel_digest_fini(struct selabel_digest *ptr)
+{
+	int i;
+
+	free(ptr->digest);
+	free(ptr->hashbuf);
+
+	if (ptr->specfile_list) {
+		for (i = 0; ptr->specfile_list[i]; i++)
+			free(ptr->specfile_list[i]);
+		free(ptr->specfile_list);
+	}
+	free(ptr);
+}
+
 /*
  * Validation functions
  */
@@ -273,6 +335,7 @@ struct selabel_handle *selabel_open(unsigned int backend,
 
 	rec->subs = NULL;
 	rec->dist_subs = NULL;
+	rec->digest = selabel_is_digest_set(opts, nopts, rec->digest);
 
 	if ((*initfuncs[backend])(rec, opts, nopts)) {
 		free(rec);
@@ -378,10 +441,28 @@ enum selabel_cmp_result selabel_cmp(struct selabel_handle *h1,
 	return h1->func_cmp(h1, h2);
 }
 
+int selabel_digest(struct selabel_handle *rec,
+				    unsigned char **digest, size_t *digest_len,
+				    char ***specfiles, size_t *num_specfiles)
+{
+	if (!rec->digest) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	*digest = rec->digest->digest;
+	*digest_len = DIGEST_SPECFILE_SIZE;
+	*specfiles = rec->digest->specfile_list;
+	*num_specfiles = rec->digest->specfile_cnt;
+	return 0;
+}
+
 void selabel_close(struct selabel_handle *rec)
 {
 	selabel_subs_fini(rec->subs);
 	selabel_subs_fini(rec->dist_subs);
+	if (rec->digest)
+		selabel_digest_fini(rec->digest);
 	rec->func_close(rec);
 	free(rec->spec_file);
 	free(rec);

libselinux/src/label_android_property.c

@@ -199,7 +199,12 @@ static int init(struct selabel_handle *rec, const struct selinux_opt *opts,
 
 	qsort(data->spec_arr, data->nspec, sizeof(struct spec), cmp);
 
-	status = 0;
+	status = digest_add_specfile(rec->digest, fp, NULL, sb.st_size, path);
+	if (status)
+		goto finish;
+
+	status = digest_gen_hash(rec->digest);
+
 finish:
 	fclose(fp);
 	return status;

libselinux/src/label_db.c

@@ -244,6 +244,7 @@ db_init(const struct selinux_opt *opts, unsigned nopts,
 	size_t		line_len = 0;
 	unsigned int	line_num = 0;
 	unsigned int	i;
+	struct stat sb;
 
 	/*
 	 * Initialize catalog data structure
@@ -280,6 +281,12 @@ db_init(const struct selinux_opt *opts, unsigned nopts,
 		free(catalog);
 		return NULL;
 	}
+	if (fstat(fileno(filp), &sb) < 0)
+		return NULL;
+	if (!S_ISREG(sb.st_mode)) {
+		errno = EINVAL;
+		return NULL;
+	}
 	rec->spec_file = strdup(path);
 
 	/*
@@ -312,6 +319,12 @@ db_init(const struct selinux_opt *opts, unsigned nopts,
 	}
 	free(line_buf);
 
+	if (digest_add_specfile(rec->digest, filp, NULL, sb.st_size, path) < 0)
+		goto out_error;
+
+	if (digest_gen_hash(rec->digest) < 0)
+		goto out_error;
+
 	fclose(filp);
 
 	return catalog;