nfsd encodes "connectable" file handles for the subtree_check feature.
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 "connectable".
Note that decoding a "connectable" file handle with open_by_handle_at(2)
is not guarandteed to return a "connected" fd (i.e. fd with known path).
A new opt-in API would be needed to guarantee a "connected" fd.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/fhandle.c | 24 ++++++++++++++++++++----
include/uapi/linux/fcntl.h | 1 +
2 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/fs/fhandle.c b/fs/fhandle.c
index 8cb665629f4a..956d9b25d4f7 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -31,6 +31,11 @@ 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;
+ /* Do not encode a connectable handle for a disconnected dentry */
+ if (fh_flags & EXPORT_FH_CONNECTABLE &&
+ path->dentry->d_flags & DCACHE_DISCONNECTED)
+ return -EACCES;
+
if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
return -EFAULT;
@@ -45,7 +50,7 @@ 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);
@@ -109,15 +114,26 @@ 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.
+ */
+ if (flag & AT_HANDLE_CONNECTABLE && flag & AT_HANDLE_FID)
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);
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 87e2dec79fea..56ff2100e021 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -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
--
2.34.1
