[PATCH] ceph: fix allocation under spinlock in mount option parsing

[Jeff Layton]

Al and syzbot reported that 4fbc0c711b24 (ceph: remove the extra slashes
in the server path) had caused a regression where an allocation could be
done under spinlock.

Fix this by keeping a canonicalized version of the path in the mount
options. Then we can simply compare those without making copies at all
during the comparison.

Fixes: 4fbc0c711b24 ("ceph: remove the extra slashes in the server path")
Reported-by: syzbot+98704a51af8e3d9425a9@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 fs/ceph/super.c | 170 ++++++++++++++++++++++--------------------------
 fs/ceph/super.h |   1 +
 2 files changed, 79 insertions(+), 92 deletions(-)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 5fa28e98d2b8..196d547c7054 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -208,6 +208,69 @@ struct ceph_parse_opts_ctx {
 	struct ceph_mount_options	*opts;
 };
 
+/**
+ * canonicalize_path - Remove the extra slashes in the server path
+ * @server_path: the server path and could be NULL
+ *
+ * Return NULL if the path is NULL or only consists of "/", or a string
+ * without any extra slashes including the leading slash(es) and the
+ * slash(es) at the end of the server path, such as:
+ * "//dir1////dir2///" --> "dir1/dir2"
+ */
+static char *canonicalize_path(const char *server_path)
+{
+	const char *path = server_path;
+	const char *cur, *end;
+	char *buf, *p;
+	int len;
+
+	/* remove all the leading slashes */
+	while (*path == '/')
+		path++;
+
+	/* if the server path only consists of slashes */
+	if (*path == '\0')
+		return NULL;
+
+	len = strlen(path);
+
+	buf = kmalloc(len + 1, GFP_KERNEL);
+	if (!buf)
+		return ERR_PTR(-ENOMEM);
+
+	end = path + len;
+	p = buf;
+	do {
+		cur = strchr(path, '/');
+		if (!cur)
+			cur = end;
+
+		len = cur - path;
+
+		/* including one '/' */
+		if (cur != end)
+			len += 1;
+
+		memcpy(p, path, len);
+		p += len;
+
+		while (cur <= end && *cur == '/')
+			cur++;
+		path = cur;
+	} while (path < end);
+
+	*p = '\0';
+
+	/*
+	 * remove the last slash if there has and just to make sure that
+	 * we will get something like "dir1/dir2"
+	 */
+	if (*(--p) == '/')
+		*p = '\0';
+
+	return buf;
+}
+
 /*
  * Parse the source parameter.  Distinguish the server list from the path.
  *
@@ -230,15 +293,23 @@ static int ceph_parse_source(struct fs_parameter *param, struct fs_context *fc)
 
 	dev_name_end = strchr(dev_name, '/');
 	if (dev_name_end) {
-		kfree(fsopt->server_path);
 
 		/*
 		 * The server_path will include the whole chars from userland
 		 * including the leading '/'.
 		 */
+		kfree(fsopt->server_path);
 		fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
 		if (!fsopt->server_path)
 			return -ENOMEM;
+
+		kfree(fsopt->canon_path);
+		fsopt->canon_path = canonicalize_path(fsopt->server_path);
+		if (fsopt->canon_path && IS_ERR(fsopt->canon_path)) {
+			ret = PTR_ERR(fsopt->canon_path);
+			fsopt->canon_path = NULL;
+			return ret;
+		}
 	} else {
 		dev_name_end = dev_name + strlen(dev_name);
 	}
@@ -447,6 +518,7 @@ static void destroy_mount_options(struct ceph_mount_options *args)
 	kfree(args->snapdir_name);
 	kfree(args->mds_namespace);
 	kfree(args->server_path);
+	kfree(args->canon_path);
 	kfree(args->fscache_uniq);
 	kfree(args);
 }
@@ -462,73 +534,6 @@ static int strcmp_null(const char *s1, const char *s2)
 	return strcmp(s1, s2);
 }
 
-/**
- * path_remove_extra_slash - Remove the extra slashes in the server path
- * @server_path: the server path and could be NULL
- *
- * Return NULL if the path is NULL or only consists of "/", or a string
- * without any extra slashes including the leading slash(es) and the
- * slash(es) at the end of the server path, such as:
- * "//dir1////dir2///" --> "dir1/dir2"
- */
-static char *path_remove_extra_slash(const char *server_path)
-{
-	const char *path = server_path;
-	const char *cur, *end;
-	char *buf, *p;
-	int len;
-
-	/* if the server path is omitted */
-	if (!path)
-		return NULL;
-
-	/* remove all the leading slashes */
-	while (*path == '/')
-		path++;
-
-	/* if the server path only consists of slashes */
-	if (*path == '\0')
-		return NULL;
-
-	len = strlen(path);
-
-	buf = kmalloc(len + 1, GFP_KERNEL);
-	if (!buf)
-		return ERR_PTR(-ENOMEM);
-
-	end = path + len;
-	p = buf;
-	do {
-		cur = strchr(path, '/');
-		if (!cur)
-			cur = end;
-
-		len = cur - path;
-
-		/* including one '/' */
-		if (cur != end)
-			len += 1;
-
-		memcpy(p, path, len);
-		p += len;
-
-		while (cur <= end && *cur == '/')
-			cur++;
-		path = cur;
-	} while (path < end);
-
-	*p = '\0';
-
-	/*
-	 * remove the last slash if there has and just to make sure that
-	 * we will get something like "dir1/dir2"
-	 */
-	if (*(--p) == '/')
-		*p = '\0';
-
-	return buf;
-}
-
 static int compare_mount_options(struct ceph_mount_options *new_fsopt,
 				 struct ceph_options *new_opt,
 				 struct ceph_fs_client *fsc)
@@ -536,7 +541,6 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
 	struct ceph_mount_options *fsopt1 = new_fsopt;
 	struct ceph_mount_options *fsopt2 = fsc->mount_options;
 	int ofs = offsetof(struct ceph_mount_options, snapdir_name);
-	char *p1, *p2;
 	int ret;
 
 	ret = memcmp(fsopt1, fsopt2, ofs);
@@ -546,21 +550,12 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
 	ret = strcmp_null(fsopt1->snapdir_name, fsopt2->snapdir_name);
 	if (ret)
 		return ret;
+
 	ret = strcmp_null(fsopt1->mds_namespace, fsopt2->mds_namespace);
 	if (ret)
 		return ret;
 
-	p1 = path_remove_extra_slash(fsopt1->server_path);
-	if (IS_ERR(p1))
-		return PTR_ERR(p1);
-	p2 = path_remove_extra_slash(fsopt2->server_path);
-	if (IS_ERR(p2)) {
-		kfree(p1);
-		return PTR_ERR(p2);
-	}
-	ret = strcmp_null(p1, p2);
-	kfree(p1);
-	kfree(p2);
+	ret = strcmp_null(fsopt1->canon_path, fsopt2->canon_path);
 	if (ret)
 		return ret;
 
@@ -963,7 +958,9 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
 	mutex_lock(&fsc->client->mount_mutex);
 
 	if (!fsc->sb->s_root) {
-		const char *path, *p;
+		const char *path = fsc->mount_options->canon_path ?
+					fsc->mount_options->canon_path : "";
+
 		err = __ceph_open_session(fsc->client, started);
 		if (err < 0)
 			goto out;
@@ -975,22 +972,11 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
 				goto out;
 		}
 
-		p = path_remove_extra_slash(fsc->mount_options->server_path);
-		if (IS_ERR(p)) {
-			err = PTR_ERR(p);
-			goto out;
-		}
-		/* if the server path is omitted or just consists of '/' */
-		if (!p)
-			path = "";
-		else
-			path = p;
 		dout("mount opening path '%s'\n", path);
 
 		ceph_fs_debugfs_init(fsc);
 
 		root = open_root_dentry(fsc, path, started);
-		kfree(p);
 		if (IS_ERR(root)) {
 			err = PTR_ERR(root);
 			goto out;
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index e8f891770f9d..70aa32cfb64d 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -94,6 +94,7 @@ struct ceph_mount_options {
 	char *snapdir_name;   /* default ".snap" */
 	char *mds_namespace;  /* default NULL */
 	char *server_path;    /* default  "/" */
+	char *canon_path;     /* default "/" */
 	char *fscache_uniq;   /* default NULL */
 };
 
-- 
2.24.1