[PATCH RFC 5/6] exportfs: add permission method

Christian Brauner
2024-11-29T13:39:33Z

This allows filesystems such as pidfs to provide their custom permission
checks.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
fs/fhandle.c | 21 +++++++--------------
include/linux/exportfs.h | 17 ++++++++++++++++-
2 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/fs/fhandle.c b/fs/fhandle.c
index 031ad5592a0beabcc299436f037ad5fe626332e6..23491094032ec037066a271873ea8ff794616bee 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -187,17 +187,6 @@ static int get_path_from_fd(int fd, struct path *root)
return 0;
}

-enum handle_to_path_flags {
- HANDLE_CHECK_PERMS = (1 << 0),
- HANDLE_CHECK_SUBTREE = (1 << 1),
-};
-
-struct handle_to_path_ctx {
- struct path root;
- enum handle_to_path_flags flags;
- unsigned int fh_flags;
-};
-
static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
{
struct handle_to_path_ctx *ctx = context;
@@ -335,15 +324,19 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
struct file_handle f_handle;
struct file_handle *handle = NULL;
struct handle_to_path_ctx ctx = {};
+ const struct export_operations *eops;

retval = get_path_from_fd(mountdirfd, &ctx.root);
if (retval)
goto out_err;

- if (!may_decode_fh(&ctx, o_flags)) {
- retval = -EPERM;
+ eops = ctx.root.mnt->mnt_sb->s_export_op;
+ if (eops && eops->permission)
+ retval = eops->permission(&ctx, o_flags);
+ else
+ retval = may_decode_fh(&ctx, o_flags);
+ if (retval)
goto out_path;
- }

if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
retval = -EFAULT;
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index c69b79b64466d5bc32ffe9b2796a388130fe72d8..a087606ace194ccc9d1250f990ce55627aaf8dc5 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -3,6 +3,7 @@
#define LINUX_EXPORTFS_H 1

#include <linux/types.h>
+#include <linux/path.h>

struct dentry;
struct iattr;
@@ -10,7 +11,6 @@ struct inode;
struct iomap;
struct super_block;
struct vfsmount;
-struct path;

/* limit the handle size to NFSv4 handle size now */
#define MAX_HANDLE_SZ 128
@@ -157,6 +157,17 @@ struct fid {
};
};

+enum handle_to_path_flags {
+ HANDLE_CHECK_PERMS = (1 << 0),
+ HANDLE_CHECK_SUBTREE = (1 << 1),
+};
+
+struct handle_to_path_ctx {
+ struct path root;
+ enum handle_to_path_flags flags;
+ unsigned int fh_flags;
+};
+
#define EXPORT_FH_CONNECTABLE 0x1 /* Encode file handle with parent */
#define EXPORT_FH_FID 0x2 /* File handle may be non-decodeable */
#define EXPORT_FH_DIR_ONLY 0x4 /* Only decode file handle for a directory */
@@ -226,6 +237,9 @@ struct fid {
* is also a directory. In the event that it cannot be found, or storage
* space cannot be allocated, a %ERR_PTR should be returned.
*
+ * permission:
+ * Allow filesystems to specify a custom permission function.
+ *
* open:
* Allow filesystems to specify a custom open function.
*
@@ -255,6 +269,7 @@ struct export_operations {
bool write, u32 *device_generation);
int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
int nr_iomaps, struct iattr *iattr);
+ int (*permission)(struct handle_to_path_ctx *ctx, unsigned int oflags);
struct file * (*open)(struct path *path, unsigned int oflags);
#define EXPORT_OP_NOWCC (0x1) /* don't collect v3 wcc data */
#define EXPORT_OP_NOSUBTREECHK (0x2) /* no subtree checking */

--
2.45.2