libmount: fix access() utab write test

The commit c08396c7691e1e6a04b6b45892e7e4612ceed8d7 replaces
open(O_CREATE) with ecaccess(). Unfortunately, another code depends on
the original behavior.

* let's make utab when really necessary rather than in the try_write() test

* __mnt_new_table_from_file() returns NULL if tab-file does not
 exists. This is incorrect for tab_update.c stuff. We need empty table
 in this case.

* we can check /run/mount/ directory for write access if
  eaccess(filename) return ENOENT (because file does not exist)

Signed-off-by: Karel Zak <kzak@redhat.com>

4 files changed, 42 insertions, 20 deletions

diff --git a/libmount/src/mountP.h b/libmount/src/mountP.h
index e01de337d..b00426d67 100644
--- a/libmount/src/mountP.h
+++ b/libmount/src/mountP.h
@@ -242,7 +242,7 @@ struct libmnt_table {
 	void		*userdata;
 };
 
-extern struct libmnt_table *__mnt_new_table_from_file(const char *filename, int fmt);
+extern struct libmnt_table *__mnt_new_table_from_file(const char *filename, int fmt, int empty_for_enoent);
 
 /*
  * Tab file format
diff --git a/libmount/src/tab_parse.c b/libmount/src/tab_parse.c
index b17a22913..02dd0c961 100644
--- a/libmount/src/tab_parse.c
+++ b/libmount/src/tab_parse.c
@@ -838,7 +838,7 @@ int mnt_table_parse_dir(struct libmnt_table *tb, const char *dirname)
 	return __mnt_table_parse_dir(tb, dirname);
 }
 
-struct libmnt_table *__mnt_new_table_from_file(const char *filename, int fmt)
+struct libmnt_table *__mnt_new_table_from_file(const char *filename, int fmt, int empty_for_enoent)
 {
 	struct libmnt_table *tb;
 	struct stat st;
@@ -846,7 +846,8 @@ struct libmnt_table *__mnt_new_table_from_file(const char *filename, int fmt)
 	if (!filename)
 		return NULL;
 	if (stat(filename, &st))
-		return NULL;
+		return empty_for_enoent ? mnt_new_table() : NULL;
+
 	tb = mnt_new_table();
 	if (tb) {
 		DBG(TAB, ul_debugobj(tb, "new tab for file: %s", filename));
@@ -875,7 +876,7 @@ struct libmnt_table *mnt_new_table_from_file(const char *filename)
 	if (!filename)
 		return NULL;
 
-	return __mnt_new_table_from_file(filename, MNT_FMT_GUESS);
+	return __mnt_new_table_from_file(filename, MNT_FMT_GUESS, 0);
 }
 
 /**
diff --git a/libmount/src/tab_update.c b/libmount/src/tab_update.c
index e95713301..23a5a8bc5 100644
--- a/libmount/src/tab_update.c
+++ b/libmount/src/tab_update.c
@@ -571,6 +571,7 @@ leave:
 
 	unlink(uq);	/* be paranoid */
 	free(uq);
+	DBG(UPDATE, ul_debugobj(upd, "%s: done [rc=%d]", upd->filename, rc));
 	return rc;
 }
 
@@ -699,7 +700,7 @@ static int update_add_entry(struct libmnt_update *upd, struct libmnt_lock *lc)
 		return -MNT_ERR_LOCK;
 
 	tb = __mnt_new_table_from_file(upd->filename,
-			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB);
+			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB, 1);
 	if (tb)
 		rc = add_file_entry(tb, upd);
 	if (lc)
@@ -725,7 +726,7 @@ static int update_remove_entry(struct libmnt_update *upd, struct libmnt_lock *lc
 		return -MNT_ERR_LOCK;
 
 	tb = __mnt_new_table_from_file(upd->filename,
-			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB);
+			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB, 1);
 	if (tb) {
 		struct libmnt_fs *rem = mnt_table_find_target(tb, upd->target, MNT_ITER_BACKWARD);
 		if (rem) {
@@ -754,7 +755,7 @@ static int update_modify_target(struct libmnt_update *upd, struct libmnt_lock *l
 		return -MNT_ERR_LOCK;
 
 	tb = __mnt_new_table_from_file(upd->filename,
-			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB);
+			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB, 1);
 	if (tb) {
 		struct libmnt_fs *cur = mnt_table_find_target(tb,
 				mnt_fs_get_srcpath(upd->fs), MNT_ITER_BACKWARD);
@@ -791,7 +792,7 @@ static int update_modify_options(struct libmnt_update *upd, struct libmnt_lock *
 		return -MNT_ERR_LOCK;
 
 	tb = __mnt_new_table_from_file(upd->filename,
-			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB);
+			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB, 1);
 	if (tb) {
 		struct libmnt_fs *cur = mnt_table_find_target(tb,
 					mnt_fs_get_target(fs),
@@ -894,7 +895,7 @@ int mnt_update_already_done(struct libmnt_update *upd, struct libmnt_lock *lc)
 	}
 
 	tb = __mnt_new_table_from_file(upd->filename,
-			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB);
+			upd->userspace_only ? MNT_FMT_UTAB : MNT_FMT_MTAB, 1);
 	if (lc)
 		mnt_unlock_file(lc);
 	if (!tb)
diff --git a/libmount/src/utils.c b/libmount/src/utils.c
index 711d1683e..5db5494d3 100644
--- a/libmount/src/utils.c
+++ b/libmount/src/utils.c
@@ -645,18 +645,37 @@ done:
 	return rc;
 }
 
-static int try_write(const char *filename)
+static int try_write(const char *filename, const char *directory)
 {
 	int rc = 0;
 
 	if (!filename)
 		return -EINVAL;
 
+	DBG(UTILS, ul_debug("try write %s dir: %s", filename, directory));
+
 #ifdef HAVE_EACCESS
-	if (eaccess(filename, R_OK|W_OK) != 0)
-		rc = -errno;
-#else
+	/* Try eaccess() first, because open() is overkill, may be monitored by
+	 * audit and we don't want to fill logs by our checks...
+	 */
+	if (eaccess(filename, R_OK|W_OK) == 0) {
+		DBG(UTILS, ul_debug(" access OK"));
+		return 0;
+	} else if (errno != ENOENT) {
+		DBG(UTILS, ul_debug(" access FAILED"));
+		return -errno;
+	} else if (directory) {
+		/* file does not exist; try if directory is writable */
+		if (eaccess(directory, R_OK|W_OK) != 0)
+			rc = -errno;
+
+		DBG(UTILS, ul_debug(" access %s [%s]", rc ? "FAILED" : "OK", directory));
+		return rc;
+	} else
+#endif
 	{
+		DBG(UTILS, ul_debug(" doing open-write test"));
+
 		int fd = open(filename, O_RDWR|O_CREAT|O_CLOEXEC,
 			    S_IWUSR|S_IRUSR|S_IRGRP|S_IROTH);
 		if (fd < 0)
@@ -664,7 +683,6 @@ static int try_write(const char *filename)
 		else
 			close(fd);
 	}
-#endif
 	return rc;
 }
 
@@ -698,7 +716,7 @@ int mnt_has_regular_mtab(const char **mtab, int *writable)
 		/* file exists */
 		if (S_ISREG(st.st_mode)) {
 			if (writable)
-				*writable = !try_write(filename);
+				*writable = !try_write(filename, NULL);
 			DBG(UTILS, ul_debug("%s: writable", filename));
 			return 1;
 		}
@@ -707,7 +725,7 @@ int mnt_has_regular_mtab(const char **mtab, int *writable)
 
 	/* try to create the file */
 	if (writable) {
-		*writable = !try_write(filename);
+		*writable = !try_write(filename, NULL);
 		if (*writable) {
 			DBG(UTILS, ul_debug("%s: writable", filename));
 			return 1;
@@ -747,7 +765,7 @@ int mnt_has_regular_utab(const char **utab, int *writable)
 		/* file exists */
 		if (S_ISREG(st.st_mode)) {
 			if (writable)
-				*writable = !try_write(filename);
+				*writable = !try_write(filename, NULL);
 			return 1;
 		}
 		goto done;	/* it's not a regular file */
@@ -764,11 +782,13 @@ int mnt_has_regular_utab(const char **utab, int *writable)
 		rc = mkdir(dirname, S_IWUSR|
 				    S_IRUSR|S_IRGRP|S_IROTH|
 				    S_IXUSR|S_IXGRP|S_IXOTH);
-		free(dirname);
-		if (rc && errno != EEXIST)
+		if (rc && errno != EEXIST) {
+			free(dirname);
 			goto done;			/* probably EACCES */
+		}
 
-		*writable = !try_write(filename);
+		*writable = !try_write(filename, dirname);
+		free(dirname);
 		if (*writable)
 			return 1;
 	}