From: Aleksa Sarai <cyphar@cyphar.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
Chuck Lever <chuck.lever@oracle.com>,
Jeff Layton <jlayton@kernel.org>,
Amir Goldstein <amir73il@gmail.com>,
Alexander Aring <alex.aring@gmail.com>
Cc: linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
linux-kernel@vger.kernel.org, Aleksa Sarai <cyphar@cyphar.com>
Subject: [PATCH RFC] fhandle: expose u64 mount id to name_to_handle_at(2)
Date: Mon, 20 May 2024 17:35:49 -0400 [thread overview]
Message-ID: <20240520-exportfs-u64-mount-id-v1-1-f55fd9215b8e@cyphar.com> (raw)
Now that we have stabilised the unique 64-bit mount ID interface in
statx, we can now provide a race-free way for name_to_handle_at(2) to
provide a file handle and corresponding mount without needing to worry
about racing with /proc/mountinfo parsing.
As with AT_HANDLE_FID, AT_HANDLE_UNIQUE_MNT_ID reuses a statx AT_* bit
that doesn't make sense for name_to_handle_at(2).
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
fs/fhandle.c | 27 +++++++++++++++++++--------
include/uapi/linux/fcntl.h | 2 ++
2 files changed, 21 insertions(+), 8 deletions(-)
diff --git a/fs/fhandle.c b/fs/fhandle.c
index 8a7f86c2139a..6bc7ffccff8c 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -16,7 +16,8 @@
static long do_sys_name_to_handle(const struct path *path,
struct file_handle __user *ufh,
- int __user *mnt_id, int fh_flags)
+ void __user *mnt_id, bool unique_mntid,
+ int fh_flags)
{
long retval;
struct file_handle f_handle;
@@ -69,10 +70,16 @@ static long do_sys_name_to_handle(const struct path *path,
} else
retval = 0;
/* copy the mount id */
- if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) ||
- copy_to_user(ufh, handle,
- struct_size(handle, f_handle, handle_bytes)))
- retval = -EFAULT;
+ if (unique_mntid)
+ retval = put_user(real_mount(path->mnt)->mnt_id_unique,
+ (u64 __user *) mnt_id);
+ else
+ retval = put_user(real_mount(path->mnt)->mnt_id,
+ (int __user *) mnt_id);
+ /* copy the handle */
+ if (!retval)
+ retval = copy_to_user(ufh, handle,
+ struct_size(handle, f_handle, handle_bytes));
kfree(handle);
return retval;
}
@@ -83,6 +90,7 @@ static long do_sys_name_to_handle(const struct path *path,
* @name: name that should be converted to handle.
* @handle: resulting file handle
* @mnt_id: mount id of the file system containing the file
+ * (u64 if AT_HANDLE_UNIQUE_MNT_ID, otherwise int)
* @flag: flag value to indicate whether to follow symlink or not
* and whether a decodable file handle is required.
*
@@ -92,7 +100,7 @@ static long do_sys_name_to_handle(const struct path *path,
* value required.
*/
SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
- struct file_handle __user *, handle, int __user *, mnt_id,
+ struct file_handle __user *, handle, void __user *, mnt_id,
int, flag)
{
struct path path;
@@ -100,7 +108,8 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
int fh_flags;
int err;
- if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID))
+ if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID |
+ AT_HANDLE_UNIQUE_MNT_ID))
return -EINVAL;
lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
@@ -109,7 +118,9 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
lookup_flags |= LOOKUP_EMPTY;
err = user_path_at(dfd, name, lookup_flags, &path);
if (!err) {
- err = do_sys_name_to_handle(&path, handle, mnt_id, fh_flags);
+ err = do_sys_name_to_handle(&path, handle, mnt_id,
+ flag & AT_HANDLE_UNIQUE_MNT_ID,
+ fh_flags);
path_put(&path);
}
return err;
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index c0bcc185fa48..fda970f92fba 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -118,6 +118,8 @@
#define AT_HANDLE_FID AT_REMOVEDIR /* file handle is needed to
compare object identity and may not
be usable to open_by_handle_at(2) */
+#define AT_HANDLE_UNIQUE_MNT_ID AT_STATX_FORCE_SYNC /* returned mount id is
+ the u64 unique mount id */
#if defined(__KERNEL__)
#define AT_GETATTR_NOSEC 0x80000000
#endif
---
base-commit: 584bbf439d0fa83d728ec49f3a38c581bdc828b4
change-id: 20240515-exportfs-u64-mount-id-9ebb5c58b53c
Best regards,
--
Aleksa Sarai <cyphar@cyphar.com>
next reply other threads:[~2024-05-20 21:36 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-20 21:35 Aleksa Sarai [this message]
2024-05-20 21:53 ` [PATCH RFC] fhandle: expose u64 mount id to name_to_handle_at(2) Jeff Layton
2024-05-20 22:27 ` Aleksa Sarai
2024-05-21 5:04 ` Amir Goldstein
2024-05-21 10:42 ` Aleksa Sarai
2024-05-21 13:45 ` Christian Brauner
2024-05-21 14:11 ` Christian Brauner
2024-05-21 14:27 ` Jeff Layton
2024-05-21 16:42 ` Amir Goldstein
2024-05-23 19:16 ` Aleksa Sarai
2024-05-23 15:52 ` Aleksa Sarai
2024-05-24 12:25 ` Christian Brauner
2024-05-24 15:58 ` Aleksa Sarai
2024-05-27 0:48 ` Dave Chinner
2024-05-27 0:06 ` Dave Chinner
2024-05-27 13:39 ` Christian Brauner
2024-05-26 8:55 ` Christoph Hellwig
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