1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/syscalls.h> 3 #include <linux/slab.h> 4 #include <linux/fs.h> 5 #include <linux/file.h> 6 #include <linux/mount.h> 7 #include <linux/namei.h> 8 #include <linux/exportfs.h> 9 #include <linux/fs_struct.h> 10 #include <linux/fsnotify.h> 11 #include <linux/personality.h> 12 #include <linux/uaccess.h> 13 #include <linux/compat.h> 14 #include "internal.h" 15 #include "mount.h" 16 17 static long do_sys_name_to_handle(const struct path *path, 18 struct file_handle __user *ufh, 19 int __user *mnt_id, int fh_flags) 20 { 21 long retval; 22 struct file_handle f_handle; 23 int handle_dwords, handle_bytes; 24 struct file_handle *handle = NULL; 25 26 /* 27 * We need to make sure whether the file system support decoding of 28 * the file handle if decodeable file handle was requested. 29 * Otherwise, even empty export_operations are sufficient to opt-in 30 * to encoding FIDs. 31 */ 32 if (!path->dentry->d_sb->s_export_op || 33 (!(fh_flags & EXPORT_FH_FID) && 34 !path->dentry->d_sb->s_export_op->fh_to_dentry)) 35 return -EOPNOTSUPP; 36 37 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) 38 return -EFAULT; 39 40 if (f_handle.handle_bytes > MAX_HANDLE_SZ) 41 return -EINVAL; 42 43 handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes, 44 GFP_KERNEL); 45 if (!handle) 46 return -ENOMEM; 47 48 /* convert handle size to multiple of sizeof(u32) */ 49 handle_dwords = f_handle.handle_bytes >> 2; 50 51 /* we ask for a non connectable maybe decodeable file handle */ 52 retval = exportfs_encode_fh(path->dentry, 53 (struct fid *)handle->f_handle, 54 &handle_dwords, fh_flags); 55 handle->handle_type = retval; 56 /* convert handle size to bytes */ 57 handle_bytes = handle_dwords * sizeof(u32); 58 handle->handle_bytes = handle_bytes; 59 if ((handle->handle_bytes > f_handle.handle_bytes) || 60 (retval == FILEID_INVALID) || (retval == -ENOSPC)) { 61 /* As per old exportfs_encode_fh documentation 62 * we could return ENOSPC to indicate overflow 63 * But file system returned 255 always. So handle 64 * both the values 65 */ 66 /* 67 * set the handle size to zero so we copy only 68 * non variable part of the file_handle 69 */ 70 handle_bytes = 0; 71 retval = -EOVERFLOW; 72 } else 73 retval = 0; 74 /* copy the mount id */ 75 if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) || 76 copy_to_user(ufh, handle, 77 sizeof(struct file_handle) + handle_bytes)) 78 retval = -EFAULT; 79 kfree(handle); 80 return retval; 81 } 82 83 /** 84 * sys_name_to_handle_at: convert name to handle 85 * @dfd: directory relative to which name is interpreted if not absolute 86 * @name: name that should be converted to handle. 87 * @handle: resulting file handle 88 * @mnt_id: mount id of the file system containing the file 89 * @flag: flag value to indicate whether to follow symlink or not 90 * and whether a decodable file handle is required. 91 * 92 * @handle->handle_size indicate the space available to store the 93 * variable part of the file handle in bytes. If there is not 94 * enough space, the field is updated to return the minimum 95 * value required. 96 */ 97 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name, 98 struct file_handle __user *, handle, int __user *, mnt_id, 99 int, flag) 100 { 101 struct path path; 102 int lookup_flags; 103 int fh_flags; 104 int err; 105 106 if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID)) 107 return -EINVAL; 108 109 lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0; 110 fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0; 111 if (flag & AT_EMPTY_PATH) 112 lookup_flags |= LOOKUP_EMPTY; 113 err = user_path_at(dfd, name, lookup_flags, &path); 114 if (!err) { 115 err = do_sys_name_to_handle(&path, handle, mnt_id, fh_flags); 116 path_put(&path); 117 } 118 return err; 119 } 120 121 static struct vfsmount *get_vfsmount_from_fd(int fd) 122 { 123 struct vfsmount *mnt; 124 125 if (fd == AT_FDCWD) { 126 struct fs_struct *fs = current->fs; 127 spin_lock(&fs->lock); 128 mnt = mntget(fs->pwd.mnt); 129 spin_unlock(&fs->lock); 130 } else { 131 struct fd f = fdget(fd); 132 if (!f.file) 133 return ERR_PTR(-EBADF); 134 mnt = mntget(f.file->f_path.mnt); 135 fdput(f); 136 } 137 return mnt; 138 } 139 140 static int vfs_dentry_acceptable(void *context, struct dentry *dentry) 141 { 142 return 1; 143 } 144 145 static int do_handle_to_path(int mountdirfd, struct file_handle *handle, 146 struct path *path) 147 { 148 int retval = 0; 149 int handle_dwords; 150 151 path->mnt = get_vfsmount_from_fd(mountdirfd); 152 if (IS_ERR(path->mnt)) { 153 retval = PTR_ERR(path->mnt); 154 goto out_err; 155 } 156 /* change the handle size to multiple of sizeof(u32) */ 157 handle_dwords = handle->handle_bytes >> 2; 158 path->dentry = exportfs_decode_fh(path->mnt, 159 (struct fid *)handle->f_handle, 160 handle_dwords, handle->handle_type, 161 vfs_dentry_acceptable, NULL); 162 if (IS_ERR(path->dentry)) { 163 retval = PTR_ERR(path->dentry); 164 goto out_mnt; 165 } 166 return 0; 167 out_mnt: 168 mntput(path->mnt); 169 out_err: 170 return retval; 171 } 172 173 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh, 174 struct path *path) 175 { 176 int retval = 0; 177 struct file_handle f_handle; 178 struct file_handle *handle = NULL; 179 180 /* 181 * With handle we don't look at the execute bit on the 182 * directory. Ideally we would like CAP_DAC_SEARCH. 183 * But we don't have that 184 */ 185 if (!capable(CAP_DAC_READ_SEARCH)) { 186 retval = -EPERM; 187 goto out_err; 188 } 189 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) { 190 retval = -EFAULT; 191 goto out_err; 192 } 193 if ((f_handle.handle_bytes > MAX_HANDLE_SZ) || 194 (f_handle.handle_bytes == 0)) { 195 retval = -EINVAL; 196 goto out_err; 197 } 198 handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes, 199 GFP_KERNEL); 200 if (!handle) { 201 retval = -ENOMEM; 202 goto out_err; 203 } 204 /* copy the full handle */ 205 *handle = f_handle; 206 if (copy_from_user(&handle->f_handle, 207 &ufh->f_handle, 208 f_handle.handle_bytes)) { 209 retval = -EFAULT; 210 goto out_handle; 211 } 212 213 retval = do_handle_to_path(mountdirfd, handle, path); 214 215 out_handle: 216 kfree(handle); 217 out_err: 218 return retval; 219 } 220 221 static long do_handle_open(int mountdirfd, struct file_handle __user *ufh, 222 int open_flag) 223 { 224 long retval = 0; 225 struct path path; 226 struct file *file; 227 int fd; 228 229 retval = handle_to_path(mountdirfd, ufh, &path); 230 if (retval) 231 return retval; 232 233 fd = get_unused_fd_flags(open_flag); 234 if (fd < 0) { 235 path_put(&path); 236 return fd; 237 } 238 file = file_open_root(&path, "", open_flag, 0); 239 if (IS_ERR(file)) { 240 put_unused_fd(fd); 241 retval = PTR_ERR(file); 242 } else { 243 retval = fd; 244 fsnotify_open(file); 245 fd_install(fd, file); 246 } 247 path_put(&path); 248 return retval; 249 } 250 251 /** 252 * sys_open_by_handle_at: Open the file handle 253 * @mountdirfd: directory file descriptor 254 * @handle: file handle to be opened 255 * @flags: open flags. 256 * 257 * @mountdirfd indicate the directory file descriptor 258 * of the mount point. file handle is decoded relative 259 * to the vfsmount pointed by the @mountdirfd. @flags 260 * value is same as the open(2) flags. 261 */ 262 SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd, 263 struct file_handle __user *, handle, 264 int, flags) 265 { 266 long ret; 267 268 if (force_o_largefile()) 269 flags |= O_LARGEFILE; 270 271 ret = do_handle_open(mountdirfd, handle, flags); 272 return ret; 273 } 274 275 #ifdef CONFIG_COMPAT 276 /* 277 * Exactly like fs/open.c:sys_open_by_handle_at(), except that it 278 * doesn't set the O_LARGEFILE flag. 279 */ 280 COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd, 281 struct file_handle __user *, handle, int, flags) 282 { 283 return do_handle_open(mountdirfd, handle, flags); 284 } 285 #endif 286