Commit d1d488d8 authored by Christian Brauner's avatar Christian Brauner Committed by Linus Torvalds
Browse files

fs: add vfs_parse_fs_param_source() helper 

Add a simple helper that filesystems can use in their parameter parser
to parse the "source" parameter. A few places open-coded this function
and that already caused a bug in the cgroup v1 parser that we fixed.
Let's make it harder to get this wrong by introducing a helper which
performs all necessary checks.

Link: https://syzkaller.appspot.com/bug?id=6312526aba5beae046fdae8f00399f87aab48b12


Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarChristian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3b046272

fs/fs_context.c

+36 −18
Original line number Diff line number Diff line
@@ -79,6 +79,35 @@ static int vfs_parse_sb_flag(struct fs_context *fc, const char *key) 
	return -ENOPARAM;

}



/**

 * vfs_parse_fs_param_source - Handle setting "source" via parameter

 * @fc: The filesystem context to modify

 * @param: The parameter

 *

 * This is a simple helper for filesystems to verify that the "source" they

 * accept is sane.

 *

 * Returns 0 on success, -ENOPARAM if this is not  "source" parameter, and

 * -EINVAL otherwise. In the event of failure, supplementary error information

 *  is logged.

 */

int vfs_parse_fs_param_source(struct fs_context *fc, struct fs_parameter *param)

{

	if (strcmp(param->key, "source") != 0)

		return -ENOPARAM;



	if (param->type != fs_value_is_string)

		return invalf(fc, "Non-string source");



	if (fc->source)

		return invalf(fc, "Multiple sources");



	fc->source = param->string;

	param->string = NULL;

	return 0;

}

EXPORT_SYMBOL(vfs_parse_fs_param_source);



/**

 * vfs_parse_fs_param - Add a single parameter to a superblock config

 * @fc: The filesystem context to modify
@@ -122,15 +151,9 @@ int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param) 
	/* If the filesystem doesn't take any arguments, give it the

	 * default handling of source.

	 */

	if (strcmp(param->key, "source") == 0) {

		if (param->type != fs_value_is_string)

			return invalf(fc, "VFS: Non-string source");

		if (fc->source)

			return invalf(fc, "VFS: Multiple sources");

		fc->source = param->string;

		param->string = NULL;

		return 0;

	}

	ret = vfs_parse_fs_param_source(fc, param);

	if (ret != -ENOPARAM)

		return ret;



	return invalf(fc, "%s: Unknown parameter '%s'",

		      fc->fs_type->name, param->key);
@@ -504,16 +527,11 @@ static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param) 
	struct legacy_fs_context *ctx = fc->fs_private;

	unsigned int size = ctx->data_size;

	size_t len = 0;

	int ret;



	if (strcmp(param->key, "source") == 0) {

		if (param->type != fs_value_is_string)

			return invalf(fc, "VFS: Legacy: Non-string source");

		if (fc->source)

			return invalf(fc, "VFS: Legacy: Multiple sources");

		fc->source = param->string;

		param->string = NULL;

		return 0;

	}

	ret = vfs_parse_fs_param_source(fc, param);

	if (ret != -ENOPARAM)

		return ret;



	if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)

		return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");

include/linux/fs_context.h

+2 −0
Original line number Diff line number Diff line
@@ -139,6 +139,8 @@ extern int vfs_parse_fs_string(struct fs_context *fc, const char *key, 
extern int generic_parse_monolithic(struct fs_context *fc, void *data);

extern int vfs_get_tree(struct fs_context *fc);

extern void put_fs_context(struct fs_context *fc);

extern int vfs_parse_fs_param_source(struct fs_context *fc,

				     struct fs_parameter *param);



/*

 * sget() wrappers to be called from the ->get_tree() op.

kernel/cgroup/cgroup-v1.c

+5 −9
Original line number Diff line number Diff line
@@ -911,15 +911,11 @@ int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param) 


	opt = fs_parse(fc, cgroup1_fs_parameters, param, &result);

	if (opt == -ENOPARAM) {

		if (strcmp(param->key, "source") == 0) {

			if (param->type != fs_value_is_string)

				return invalf(fc, "Non-string source");

			if (fc->source)

				return invalf(fc, "Multiple sources not supported");

			fc->source = param->string;

			param->string = NULL;

			return 0;

		}

		int ret;



		ret = vfs_parse_fs_param_source(fc, param);

		if (ret != -ENOPARAM)

			return ret;

		for_each_subsys(ss, i) {

			if (strcmp(param->key, ss->legacy_name))

				continue;