diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c index 07ea3d62b298..4f2dd4ab4486 100644 --- a/fs/exportfs/expfs.c +++ b/fs/exportfs/expfs.c @@ -427,7 +427,7 @@ EXPORT_SYMBOL_GPL(exportfs_encode_fh); struct dentry * exportfs_decode_fh_raw(struct vfsmount *mnt, struct fid *fid, int fh_len, - int fileid_type, + int fileid_type, unsigned int flags, int (*acceptable)(void *, struct dentry *), void *context) { @@ -445,6 +445,11 @@ exportfs_decode_fh_raw(struct vfsmount *mnt, struct fid *fid, int fh_len, if (IS_ERR_OR_NULL(result)) return result; + if ((flags & EXPORT_FH_DIR_ONLY) && !d_is_dir(result)) { + err = -ENOTDIR; + goto err_result; + } + /* * If no acceptance criteria was specified by caller, a disconnected * dentry is also accepatable. Callers may use this mode to query if @@ -581,7 +586,7 @@ struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid, { struct dentry *ret; - ret = exportfs_decode_fh_raw(mnt, fid, fh_len, fileid_type, + ret = exportfs_decode_fh_raw(mnt, fid, fh_len, fileid_type, 0, acceptable, context); if (IS_ERR_OR_NULL(ret)) { if (ret == ERR_PTR(-ENOMEM)) diff --git a/fs/fhandle.c b/fs/fhandle.c index 8a7f86c2139a..6e8cea16790e 100644 --- a/fs/fhandle.c +++ b/fs/fhandle.c @@ -115,88 +115,188 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name, return err; } -static struct vfsmount *get_vfsmount_from_fd(int fd) +static int get_path_from_fd(int fd, struct path *root) { - struct vfsmount *mnt; - if (fd == AT_FDCWD) { struct fs_struct *fs = current->fs; spin_lock(&fs->lock); - mnt = mntget(fs->pwd.mnt); + *root = fs->pwd; + path_get(root); spin_unlock(&fs->lock); } else { struct fd f = fdget(fd); if (!f.file) - return ERR_PTR(-EBADF); - mnt = mntget(f.file->f_path.mnt); + return -EBADF; + *root = f.file->f_path; + path_get(root); fdput(f); } - return mnt; + + return 0; } +enum handle_to_path_flags { + HANDLE_CHECK_PERMS = (1 << 0), + HANDLE_CHECK_SUBTREE = (1 << 1), +}; + +struct handle_to_path_ctx { + struct path root; + enum handle_to_path_flags flags; + unsigned int fh_flags; +}; + static int vfs_dentry_acceptable(void *context, struct dentry *dentry) { - return 1; -} - -static int do_handle_to_path(int mountdirfd, struct file_handle *handle, - struct path *path) -{ + struct handle_to_path_ctx *ctx = context; + struct user_namespace *user_ns = current_user_ns(); + struct dentry *d, *root = ctx->root.dentry; + struct mnt_idmap *idmap = mnt_idmap(ctx->root.mnt); int retval = 0; - int handle_dwords; - path->mnt = get_vfsmount_from_fd(mountdirfd); - if (IS_ERR(path->mnt)) { - retval = PTR_ERR(path->mnt); - goto out_err; + if (!root) + return 1; + + /* Old permission model with global CAP_DAC_READ_SEARCH. */ + if (!ctx->flags) + return 1; + + /* + * It's racy as we're not taking rename_lock but we're able to ignore + * permissions and we just need an approximation whether we were able + * to follow a path to the file. + * + * It's also potentially expensive on some filesystems especially if + * there is a deep path. + */ + d = dget(dentry); + while (d != root && !IS_ROOT(d)) { + struct dentry *parent = dget_parent(d); + + /* + * We know that we have the ability to override DAC permissions + * as we've verified this earlier via CAP_DAC_READ_SEARCH. But + * we also need to make sure that there aren't any unmapped + * inodes in the path that would prevent us from reaching the + * file. + */ + if (!privileged_wrt_inode_uidgid(user_ns, idmap, + d_inode(parent))) { + dput(d); + dput(parent); + return retval; + } + + dput(d); + d = parent; } - /* change the handle size to multiple of sizeof(u32) */ - handle_dwords = handle->handle_bytes >> 2; - path->dentry = exportfs_decode_fh(path->mnt, - (struct fid *)handle->f_handle, - handle_dwords, handle->handle_type, - vfs_dentry_acceptable, NULL); - if (IS_ERR(path->dentry)) { - retval = PTR_ERR(path->dentry); - goto out_mnt; - } - return 0; -out_mnt: - mntput(path->mnt); -out_err: + + if (!(ctx->flags & HANDLE_CHECK_SUBTREE) || d == root) + retval = 1; + WARN_ON_ONCE(d != root && d != root->d_sb->s_root); + dput(d); return retval; } +static int do_handle_to_path(struct file_handle *handle, struct path *path, + struct handle_to_path_ctx *ctx) +{ + int handle_dwords; + struct vfsmount *mnt = ctx->root.mnt; + + /* change the handle size to multiple of sizeof(u32) */ + handle_dwords = handle->handle_bytes >> 2; + path->dentry = exportfs_decode_fh_raw(mnt, + (struct fid *)handle->f_handle, + handle_dwords, handle->handle_type, + ctx->fh_flags, + vfs_dentry_acceptable, ctx); + if (IS_ERR_OR_NULL(path->dentry)) { + if (path->dentry == ERR_PTR(-ENOMEM)) + return -ENOMEM; + return -ESTALE; + } + path->mnt = mntget(mnt); + return 0; +} + +/* + * Allow relaxed permissions of file handles if the caller has the + * ability to mount the filesystem or create a bind-mount of the + * provided @mountdirfd. + * + * In both cases the caller may be able to get an unobstructed way to + * the encoded file handle. If the caller is only able to create a + * bind-mount we need to verify that there are no locked mounts on top + * of it that could prevent us from getting to the encoded file. + * + * In principle, locked mounts can prevent the caller from mounting the + * filesystem but that only applies to procfs and sysfs neither of which + * support decoding file handles. + */ +static inline bool may_decode_fh(struct handle_to_path_ctx *ctx, + unsigned int o_flags) +{ + struct path *root = &ctx->root; + + /* + * Restrict to O_DIRECTORY to provide a deterministic API that avoids a + * confusing api in the face of disconnected non-dir dentries. + * + * There's only one dentry for each directory inode (VFS rule)... + */ + if (!(o_flags & O_DIRECTORY)) + return false; + + if (ns_capable(root->mnt->mnt_sb->s_user_ns, CAP_SYS_ADMIN)) + ctx->flags = HANDLE_CHECK_PERMS; + else if (is_mounted(root->mnt) && + ns_capable(real_mount(root->mnt)->mnt_ns->user_ns, + CAP_SYS_ADMIN) && + !has_locked_children(real_mount(root->mnt), root->dentry)) + ctx->flags = HANDLE_CHECK_PERMS | HANDLE_CHECK_SUBTREE; + else + return false; + + /* Are we able to override DAC permissions? */ + if (!ns_capable(current_user_ns(), CAP_DAC_READ_SEARCH)) + return false; + + ctx->fh_flags = EXPORT_FH_DIR_ONLY; + return true; +} + static int handle_to_path(int mountdirfd, struct file_handle __user *ufh, - struct path *path) + struct path *path, unsigned int o_flags) { int retval = 0; struct file_handle f_handle; struct file_handle *handle = NULL; + struct handle_to_path_ctx ctx = {}; - /* - * With handle we don't look at the execute bit on the - * directory. Ideally we would like CAP_DAC_SEARCH. - * But we don't have that - */ - if (!capable(CAP_DAC_READ_SEARCH)) { - retval = -EPERM; + retval = get_path_from_fd(mountdirfd, &ctx.root); + if (retval) goto out_err; + + if (!capable(CAP_DAC_READ_SEARCH) && !may_decode_fh(&ctx, o_flags)) { + retval = -EPERM; + goto out_path; } + if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) { retval = -EFAULT; - goto out_err; + goto out_path; } if ((f_handle.handle_bytes > MAX_HANDLE_SZ) || (f_handle.handle_bytes == 0)) { retval = -EINVAL; - goto out_err; + goto out_path; } handle = kmalloc(struct_size(handle, f_handle, f_handle.handle_bytes), GFP_KERNEL); if (!handle) { retval = -ENOMEM; - goto out_err; + goto out_path; } /* copy the full handle */ *handle = f_handle; @@ -207,10 +307,12 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh, goto out_handle; } - retval = do_handle_to_path(mountdirfd, handle, path); + retval = do_handle_to_path(handle, path, &ctx); out_handle: kfree(handle); +out_path: + path_put(&ctx.root); out_err: return retval; } @@ -223,7 +325,7 @@ static long do_handle_open(int mountdirfd, struct file_handle __user *ufh, struct file *file; int fd; - retval = handle_to_path(mountdirfd, ufh, &path); + retval = handle_to_path(mountdirfd, ufh, &path, open_flag); if (retval) return retval; diff --git a/fs/mount.h b/fs/mount.h index 4a42fc68f4cc..4adce73211ae 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -152,3 +152,4 @@ static inline void move_from_ns(struct mount *mnt, struct list_head *dt_list) } extern void mnt_cursor_del(struct mnt_namespace *ns, struct mount *cursor); +bool has_locked_children(struct mount *mnt, struct dentry *dentry); diff --git a/fs/namespace.c b/fs/namespace.c index 5a51315c6678..4386787210c7 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2078,7 +2078,7 @@ void drop_collected_mounts(struct vfsmount *mnt) namespace_unlock(); } -static bool has_locked_children(struct mount *mnt, struct dentry *dentry) +bool has_locked_children(struct mount *mnt, struct dentry *dentry) { struct mount *child; diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c index 0b75305fb5f5..dd4e11a703aa 100644 --- a/fs/nfsd/nfsfh.c +++ b/fs/nfsd/nfsfh.c @@ -247,7 +247,7 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp) dentry = dget(exp->ex_path.dentry); else { dentry = exportfs_decode_fh_raw(exp->ex_path.mnt, fid, - data_left, fileid_type, + data_left, fileid_type, 0, nfsd_acceptable, exp); if (IS_ERR_OR_NULL(dentry)) { trace_nfsd_set_fh_dentry_badhandle(rqstp, fhp, diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h index bb37ad5cc954..893a1d21dc1c 100644 --- a/include/linux/exportfs.h +++ b/include/linux/exportfs.h @@ -158,6 +158,7 @@ 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 */ /** * struct export_operations - for nfsd to communicate with file systems @@ -305,6 +306,7 @@ static inline int exportfs_encode_fid(struct inode *inode, struct fid *fid, extern struct dentry *exportfs_decode_fh_raw(struct vfsmount *mnt, struct fid *fid, int fh_len, int fileid_type, + unsigned int flags, int (*acceptable)(void *, struct dentry *), void *context); extern struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,