hostfs: fix the host directory parse when mounting.

Commit Message

Hongbo Li July 25, 2024, 6:51 a.m. UTC

hostfs not keep the host directory when mounting. When the host
directory is none (default), fc->source is used as the host root
directory, and this is wrong. Here we use `parse_monolithic` to
handle the old mount path for parsing the root directory. For new
mount path, The `parse_param` is used for the host directory parse.

Reported-and-tested-by: Maciej Żenczykowski <[e-mail]>
Fixes: cd140ce9f611 ("hostfs: convert hostfs to use the new mount API")
Link: https://lore.kernel.org/all/CANP3RGceNzwdb7w=vPf5=[e-mail]/
Cc: Christian Brauner <[e-mail]>
Signed-off-by: Hongbo Li <[e-mail]>
---
 fs/hostfs/hostfs_kern.c | 65 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 55 insertions(+), 10 deletions(-)

Comments

Christian Brauner July 26, 2024, 7:57 a.m. UTC | #1

On Thu, 25 Jul 2024 14:51:30 +0800, Hongbo Li wrote:
> hostfs not keep the host directory when mounting. When the host
> directory is none (default), fc->source is used as the host root
> directory, and this is wrong. Here we use `parse_monolithic` to
> handle the old mount path for parsing the root directory. For new
> mount path, The `parse_param` is used for the host directory parse.
> 
> 
> [...]

As mentioned somewhere else the check for param->string being empty needs to
check for empty string, not NULL. I've fixed that up.

---

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] hostfs: fix the host directory parse when mounting.
      https://git.kernel.org/vfs/vfs/c/3ab8d61f1e4a

Patch

diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index 2b532670a561..48d2a21c3380 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -17,6 +17,7 @@ 
 #include <linux/writeback.h>
 #include <linux/mount.h>
 #include <linux/fs_context.h>
+#include <linux/fs_parser.h>
 #include <linux/namei.h>
 #include "hostfs.h"
 #include <init.h>
@@ -927,7 +928,6 @@  static const struct inode_operations hostfs_link_iops = {
 static int hostfs_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	struct hostfs_fs_info *fsi = sb->s_fs_info;
-	const char *host_root = fc->source;
 	struct inode *root_inode;
 	int err;
 
@@ -941,15 +941,6 @@  static int hostfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (err)
 		return err;
 
-	/* NULL is printed as '(null)' by printf(): avoid that. */
-	if (fc->source == NULL)
-		host_root = "";
-
-	fsi->host_root_path =
-		kasprintf(GFP_KERNEL, "%s/%s", root_ino, host_root);
-	if (fsi->host_root_path == NULL)
-		return -ENOMEM;
-
 	root_inode = hostfs_iget(sb, fsi->host_root_path);
 	if (IS_ERR(root_inode))
 		return PTR_ERR(root_inode);
@@ -975,6 +966,58 @@  static int hostfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	return 0;
 }
 
+enum hostfs_parma {
+	Opt_hostfs,
+};
+
+static const struct fs_parameter_spec hostfs_param_specs[] = {
+	fsparam_string_empty("hostfs",		Opt_hostfs),
+	{}
+};
+
+static int hostfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
+{
+	struct hostfs_fs_info *fsi = fc->s_fs_info;
+	struct fs_parse_result result;
+	char *host_root;
+	int opt;
+
+	opt = fs_parse(fc, hostfs_param_specs, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_hostfs:
+		host_root = param->string;
+		if (!host_root)
+			host_root = "";
+		fsi->host_root_path =
+			kasprintf(GFP_KERNEL, "%s/%s", root_ino, host_root);
+		if (fsi->host_root_path == NULL)
+			return -ENOMEM;
+		break;
+	}
+
+	return 0;
+}
+
+static int hostfs_parse_monolithic(struct fs_context *fc, void *data)
+{
+	struct hostfs_fs_info *fsi = fc->s_fs_info;
+	char *host_root = (char *)data;
+
+	/* NULL is printed as '(null)' by printf(): avoid that. */
+	if (host_root == NULL)
+		host_root = "";
+
+	fsi->host_root_path =
+		kasprintf(GFP_KERNEL, "%s/%s", root_ino, host_root);
+	if (fsi->host_root_path == NULL)
+		return -ENOMEM;
+
+	return 0;
+}
+
 static int hostfs_fc_get_tree(struct fs_context *fc)
 {
 	return get_tree_nodev(fc, hostfs_fill_super);
@@ -992,6 +1035,8 @@  static void hostfs_fc_free(struct fs_context *fc)
 }
 
 static const struct fs_context_operations hostfs_context_ops = {
+	.parse_monolithic = hostfs_parse_monolithic,
+	.parse_param	= hostfs_parse_param,
 	.get_tree	= hostfs_fc_get_tree,
 	.free		= hostfs_fc_free,
 };