Unverified Commit c374196b authored by Amir Goldstein's avatar Amir Goldstein Committed by Christian Brauner
Browse files

fs: name_to_handle_at() support for "explicit connectable" file handles 



nfsd encodes "connectable" file handles for the subtree_check feature,
which can be resolved to an open file with a connected path.
So far, userspace nfs server could not make use of this functionality.

Introduce a new flag AT_HANDLE_CONNECTABLE to name_to_handle_at(2).
When used, the encoded file handle is "explicitly connectable".

The "explicitly connectable" file handle sets bits in the high 16bit of
the handle_type field, so open_by_handle_at(2) will know that it needs
to open a file with a connected path.

old kernels will now recognize the handle_type with high bits set,
so "explicitly connectable" file handles cannot be decoded by
open_by_handle_at(2) on old kernels.

The flag AT_HANDLE_CONNECTABLE is not allowed together with either
AT_HANDLE_FID or AT_EMPTY_PATH.

Signed-off-by: default avatarAmir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20241011090023.655623-3-amir73il@gmail.com


Fixes: 570df4e9 ("ceph: snapshot nfs re-export")
Acked-by:
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 4a530a7c

fs/fhandle.c

+43 −5
Original line number Diff line number Diff line
@@ -31,6 +31,14 @@ static long do_sys_name_to_handle(const struct path *path, 
	if (!exportfs_can_encode_fh(path->dentry->d_sb->s_export_op, fh_flags))

		return -EOPNOTSUPP;



	/*

	 * A request to encode a connectable handle for a disconnected dentry

	 * is unexpected since AT_EMPTY_PATH is not allowed.

	 */

	if (fh_flags & EXPORT_FH_CONNECTABLE &&

	    WARN_ON(path->dentry->d_flags & DCACHE_DISCONNECTED))

		return -EINVAL;



	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))

		return -EFAULT;
@@ -45,7 +53,7 @@ static long do_sys_name_to_handle(const struct path *path, 
	/* convert handle size to multiple of sizeof(u32) */

	handle_dwords = f_handle.handle_bytes >> 2;



	/* we ask for a non connectable maybe decodeable file handle */

	/* Encode a possibly decodeable/connectable file handle */

	retval = exportfs_encode_fh(path->dentry,

				    (struct fid *)handle->f_handle,

				    &handle_dwords, fh_flags);
@@ -67,8 +75,23 @@ static long do_sys_name_to_handle(const struct path *path, 
		 * non variable part of the file_handle

		 */

		handle_bytes = 0;

	} else

	} else {

		/*

		 * When asked to encode a connectable file handle, encode this

		 * property in the file handle itself, so that we later know

		 * how to decode it.

		 * For sanity, also encode in the file handle if the encoded

		 * object is a directory and verify this during decode, because

		 * decoding directory file handles is quite different than

		 * decoding connectable non-directory file handles.

		 */

		if (fh_flags & EXPORT_FH_CONNECTABLE) {

			handle->handle_type |= FILEID_IS_CONNECTABLE;

			if (d_is_dir(path->dentry))

				fh_flags |= FILEID_IS_DIR;

		}

		retval = 0;

	}

	/* copy the mount id */

	if (unique_mntid) {

		if (put_user(real_mount(path->mnt)->mnt_id_unique,
@@ -109,15 +132,30 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name, 
{

	struct path path;

	int lookup_flags;

	int fh_flags;

	int fh_flags = 0;

	int err;



	if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID |

		     AT_HANDLE_MNT_ID_UNIQUE))

		     AT_HANDLE_MNT_ID_UNIQUE | AT_HANDLE_CONNECTABLE))

		return -EINVAL;



	/*

	 * AT_HANDLE_FID means there is no intention to decode file handle

	 * AT_HANDLE_CONNECTABLE means there is an intention to decode a

	 * connected fd (with known path), so these flags are conflicting.

	 * AT_EMPTY_PATH could be used along with a dfd that refers to a

	 * disconnected non-directory, which cannot be used to encode a

	 * connectable file handle, because its parent is unknown.

	 */

	if (flag & AT_HANDLE_CONNECTABLE &&

	    flag & (AT_HANDLE_FID | AT_EMPTY_PATH))

		return -EINVAL;

	else if (flag & AT_HANDLE_FID)

		fh_flags |= EXPORT_FH_FID;

	else if (flag & AT_HANDLE_CONNECTABLE)

		fh_flags |= EXPORT_FH_CONNECTABLE;



	lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;

	fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0;

	if (flag & AT_EMPTY_PATH)

		lookup_flags |= LOOKUP_EMPTY;

	err = user_path_at(dfd, name, lookup_flags, &path);

include/linux/exportfs.h

+2 −0
Original line number Diff line number Diff line
@@ -169,6 +169,8 @@ struct fid { 
#define FILEID_USER_FLAGS(type) ((type) & FILEID_USER_FLAGS_MASK)



/* Flags supported in encoded handle_type that is exported to user */

#define FILEID_IS_CONNECTABLE	0x10000

#define FILEID_IS_DIR		0x20000

#define FILEID_VALID_USER_FLAGS	(0)



/**

include/uapi/linux/fcntl.h

+1 −0
Original line number Diff line number Diff line
@@ -153,6 +153,7 @@ 
					   object identity and may not be

					   usable with open_by_handle_at(2). */

#define AT_HANDLE_MNT_ID_UNIQUE	0x001	/* Return the u64 unique mount ID. */

#define AT_HANDLE_CONNECTABLE	0x002	/* Request a connectable file handle */



#if defined(__KERNEL__)

#define AT_GETATTR_NOSEC	0x80000000