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[92.109.99.123]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a90cbc7122esm512948866b.124.2024.09.23.01.28.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Sep 2024 01:28:34 -0700 (PDT) From: Amir Goldstein To: Jeff Layton Cc: Christian Brauner , Aleksa Sarai , Chuck Lever , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Subject: [PATCH v2 1/2] fs: name_to_handle_at() support for "explicit connectable" file handles Date: Mon, 23 Sep 2024 10:28:28 +0200 Message-Id: <20240923082829.1910210-2-amir73il@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240923082829.1910210-1-amir73il@gmail.com> References: <20240923082829.1910210-1-amir73il@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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: Amir Goldstein --- fs/fhandle.c | 53 ++++++++++++++++++++++++++++++++++---- include/linux/exportfs.h | 2 ++ include/linux/fs.h | 3 ++- include/uapi/linux/fcntl.h | 1 + 4 files changed, 53 insertions(+), 6 deletions(-) diff --git a/fs/fhandle.c b/fs/fhandle.c index 8cb665629f4a..6c87f1764235 100644 --- a/fs/fhandle.c +++ b/fs/fhandle.c @@ -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); @@ -54,6 +62,7 @@ static long do_sys_name_to_handle(const struct path *path, handle_bytes = handle_dwords * sizeof(u32); handle->handle_bytes = handle_bytes; if ((handle->handle_bytes > f_handle.handle_bytes) || + WARN_ON_ONCE(retval > FILEID_INVALID) || (retval == FILEID_INVALID) || (retval < 0)) { /* As per old exportfs_encode_fh documentation * we could return ENOSPC to indicate overflow @@ -67,8 +76,23 @@ 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) { + if (d_is_dir(path->dentry)) + fh_flags |= EXPORT_FH_DIR_ONLY; + handle->handle_flags = fh_flags; + } retval = 0; + } /* copy the mount id */ if (unique_mntid) { if (put_user(real_mount(path->mnt)->mnt_id_unique, @@ -109,15 +133,30 @@ 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); @@ -307,6 +346,10 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh, retval = -EINVAL; goto out_path; } + if (f_handle.handle_flags) { + retval = -EINVAL; + goto out_path; + } handle = kmalloc(struct_size(handle, f_handle, f_handle.handle_bytes), GFP_KERNEL); if (!handle) { diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h index 893a1d21dc1c..96b62e502f71 100644 --- a/include/linux/exportfs.h +++ b/include/linux/exportfs.h @@ -159,6 +159,8 @@ struct fid { #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 */ +/* Flags allowed in encoded handle_flags that is exported to user */ +#define EXPORT_FH_USER_FLAGS (EXPORT_FH_CONNECTABLE | EXPORT_FH_DIR_ONLY) /** * struct export_operations - for nfsd to communicate with file systems diff --git a/include/linux/fs.h b/include/linux/fs.h index 0df3e5f0dd2b..bcf8f750b309 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1071,7 +1071,8 @@ struct file { struct file_handle { __u32 handle_bytes; - int handle_type; + int handle_type:16; + int handle_flags:16; /* file identifier */ unsigned char f_handle[] __counted_by(handle_bytes); }; 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