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 = kzalloc(struct_size(handle, f_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 < 0)) { 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 if (retval == FILEID_INVALID || retval == -ENOSPC) 67 retval = -EOVERFLOW; 68 /* 69 * set the handle size to zero so we copy only 70 * non variable part of the file_handle 71 */ 72 handle_bytes = 0; 73 } else 74 retval = 0; 75 /* copy the mount id */ 76 if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) || 77 copy_to_user(ufh, handle, 78 struct_size(handle, f_handle, handle_bytes))) 79 retval = -EFAULT; 80 kfree(handle); 81 return retval; 82 } 83 84 /** 85 * sys_name_to_handle_at: convert name to handle 86 * @dfd: directory relative to which name is interpreted if not absolute 87 * @name: name that should be converted to handle. 88 * @handle: resulting file handle 89 * @mnt_id: mount id of the file system containing the file 90 * @flag: flag value to indicate whether to follow symlink or not 91 * and whether a decodable file handle is required. 92 * 93 * @handle->handle_size indicate the space available to store the 94 * variable part of the file handle in bytes. If there is not 95 * enough space, the field is updated to return the minimum 96 * value required. 97 */ 98 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name, 99 struct file_handle __user *, handle, int __user *, mnt_id, 100 int, flag) 101 { 102 struct path path; 103 int lookup_flags; 104 int fh_flags; 105 int err; 106 107 if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID)) 108 return -EINVAL; 109 110 lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0; 111 fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0; 112 if (flag & AT_EMPTY_PATH) 113 lookup_flags |= LOOKUP_EMPTY; 114 err = user_path_at(dfd, name, lookup_flags, &path); 115 if (!err) { 116 err = do_sys_name_to_handle(&path, handle, mnt_id, fh_flags); 117 path_put(&path); 118 } 119 return err; 120 } 121 122 static struct vfsmount *get_vfsmount_from_fd(int fd) 123 { 124 struct vfsmount *mnt; 125 126 if (fd == AT_FDCWD) { 127 struct fs_struct *fs = current->fs; 128 spin_lock(&fs->lock); 129 mnt = mntget(fs->pwd.mnt); 130 spin_unlock(&fs->lock); 131 } else { 132 struct fd f = fdget(fd); 133 if (!f.file) 134 return ERR_PTR(-EBADF); 135 mnt = mntget(f.file->f_path.mnt); 136 fdput(f); 137 } 138 return mnt; 139 } 140 141 static int vfs_dentry_acceptable(void *context, struct dentry *dentry) 142 { 143 return 1; 144 } 145 146 static int do_handle_to_path(int mountdirfd, struct file_handle *handle, 147 struct path *path) 148 { 149 int retval = 0; 150 int handle_dwords; 151 152 path->mnt = get_vfsmount_from_fd(mountdirfd); 153 if (IS_ERR(path->mnt)) { 154 retval = PTR_ERR(path->mnt); 155 goto out_err; 156 } 157 /* change the handle size to multiple of sizeof(u32) */ 158 handle_dwords = handle->handle_bytes >> 2; 159 path->dentry = exportfs_decode_fh(path->mnt, 160 (struct fid *)handle->f_handle, 161 handle_dwords, handle->handle_type, 162 vfs_dentry_acceptable, NULL); 163 if (IS_ERR(path->dentry)) { 164 retval = PTR_ERR(path->dentry); 165 goto out_mnt; 166 } 167 return 0; 168 out_mnt: 169 mntput(path->mnt); 170 out_err: 171 return retval; 172 } 173 174 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh, 175 struct path *path) 176 { 177 int retval = 0; 178 struct file_handle f_handle; 179 struct file_handle *handle = NULL; 180 181 /* 182 * With handle we don't look at the execute bit on the 183 * directory. Ideally we would like CAP_DAC_SEARCH. 184 * But we don't have that 185 */ 186 if (!capable(CAP_DAC_READ_SEARCH)) { 187 retval = -EPERM; 188 goto out_err; 189 } 190 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) { 191 retval = -EFAULT; 192 goto out_err; 193 } 194 if ((f_handle.handle_bytes > MAX_HANDLE_SZ) || 195 (f_handle.handle_bytes == 0)) { 196 retval = -EINVAL; 197 goto out_err; 198 } 199 handle = kmalloc(struct_size(handle, f_handle, f_handle.handle_bytes), 200 GFP_KERNEL); 201 if (!handle) { 202 retval = -ENOMEM; 203 goto out_err; 204 } 205 /* copy the full handle */ 206 *handle = f_handle; 207 if (copy_from_user(&handle->f_handle, 208 &ufh->f_handle, 209 f_handle.handle_bytes)) { 210 retval = -EFAULT; 211 goto out_handle; 212 } 213 214 retval = do_handle_to_path(mountdirfd, handle, path); 215 216 out_handle: 217 kfree(handle); 218 out_err: 219 return retval; 220 } 221 222 static long do_handle_open(int mountdirfd, struct file_handle __user *ufh, 223 int open_flag) 224 { 225 long retval = 0; 226 struct path path; 227 struct file *file; 228 int fd; 229 230 retval = handle_to_path(mountdirfd, ufh, &path); 231 if (retval) 232 return retval; 233 234 fd = get_unused_fd_flags(open_flag); 235 if (fd < 0) { 236 path_put(&path); 237 return fd; 238 } 239 file = file_open_root(&path, "", open_flag, 0); 240 if (IS_ERR(file)) { 241 put_unused_fd(fd); 242 retval = PTR_ERR(file); 243 } else { 244 retval = fd; 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