This new field is an alternative to lo_inode.fd: Either of the two must be set. In case an O_PATH FD is needed for some lo_inode, it is either taken from lo_inode.fd, if valid, or a temporary FD is opened with open_by_handle_at().
Using a file handle instead of an FD has the advantage of keeping the number of open file descriptors low. Because open_by_handle_at() requires a mount FD (i.e. a non-O_PATH FD opened on the filesystem to which the file handle refers), but every lo_fhandle only has a mount ID (as returned by name_to_handle_at()), we keep a hash map of such FDs in mount_fds (mapping ID to FD). get_file_handle(), which is added by a later patch, will ensure that every mount ID for which we have generated a handle has a corresponding entry in mount_fds. Every handle holds a strong reference to its mount FD (lo_mount_fd.refcount) so we can clean up mount FDs when they are no longer needed. release_file_handle()'s drop_mount_fd_ref parameter may look a bit strange at this point, because we always pass true for it, but it will make more sense when we start generating file handles: At that point, we will also use this function to clean up lo_fhandle object that do not yet have a strong reference to an lo_mount_fd object, and then we will need to be able to pass false for drop_mount_fd_ref. Signed-off-by: Hanna Reitz <hre...@redhat.com> --- tools/virtiofsd/passthrough_ll.c | 175 +++++++++++++++++++++++--- tools/virtiofsd/passthrough_seccomp.c | 1 + 2 files changed, 161 insertions(+), 15 deletions(-) diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index bc3b803d46..bd8fc922ea 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -88,8 +88,18 @@ struct lo_key { uint64_t mnt_id; }; +struct lo_fhandle { + union { + struct file_handle handle; + char padding[sizeof(struct file_handle) + MAX_HANDLE_SZ]; + }; + int mount_id; +}; + struct lo_inode { + /* fd or fhandle must be set (i.e. >= 0 or non-NULL, respectively) */ int fd; + struct lo_fhandle *fhandle; /* * Atomic reference count for this object. The nlookup field holds a @@ -142,6 +152,19 @@ typedef struct xattr_map_entry { unsigned int flags; } XattrMapEntry; +/* + * An O_RDONLY FD representing the mount it is on. We need this for + * open_by_handle_at(). + * + * The refcount is increased every time we store a file handle for + * this mount, and it is decreased every time we release such a stored + * file handle. + */ +struct lo_mount_fd { + int fd; + gint refcount; +}; + struct lo_data { pthread_mutex_t mutex; int sandbox; @@ -178,6 +201,10 @@ struct lo_data { /* If set, virtiofsd is responsible for setting umask during creation */ bool change_umask; int user_posix_acl, posix_acl; + + /* Maps (integer) mount IDs to lo_mount_fd objects */ + GHashTable *mount_fds; + pthread_rwlock_t mount_fds_lock; }; /** @@ -316,6 +343,93 @@ static void temp_fd_copy(const TempFd *from, TempFd *to) }; } +static void free_lo_mount_fd(gpointer data) +{ + struct lo_mount_fd *mfd = data; + + close(mfd->fd); + g_free(mfd); +} + +/** + * Frees a file handle and optionally removes its reference to the + * associated mount FD. (Passing NULL as @fh is OK.) + * + * Pass @drop_mount_fd_ref == true if and only if this handle has a + * strong reference to an lo_mount_fd object in the mount_fds hash + * table. That is always the case for file handles stored in lo_inode + * objects. + */ +static void release_file_handle(struct lo_data *lo, struct lo_fhandle *fh, + bool drop_mount_fd_ref) +{ + if (!fh) { + return; + } + + if (drop_mount_fd_ref) { + struct lo_mount_fd *mfd; + + if (pthread_rwlock_rdlock(&lo->mount_fds_lock)) { + fuse_log(FUSE_LOG_ERR, "%s(): Dropping mount FD reference failed " + "(mount ID: %i)\n", __func__, fh->mount_id); + } else { + mfd = g_hash_table_lookup(lo->mount_fds, + GINT_TO_POINTER(fh->mount_id)); + assert(mfd != NULL); + + pthread_rwlock_unlock(&lo->mount_fds_lock); + + if (g_atomic_int_dec_and_test(&mfd->refcount)) { + if (pthread_rwlock_wrlock(&lo->mount_fds_lock)) { + fuse_log(FUSE_LOG_ERR, "%s(): Dropping mount FD reference " + "failed (mount ID: %i)\n", __func__, fh->mount_id); + } else { + /* Auto-closes the FD and frees mfd */ + g_hash_table_remove(lo->mount_fds, + GINT_TO_POINTER(fh->mount_id)); + pthread_rwlock_unlock(&lo->mount_fds_lock); + } + } + } + } + + g_free(fh); +} + +/** + * Open the given file handle with the given flags. + * + * The mount FD to pass to open_by_handle_at() is taken from the + * mount_fds hash map. + * + * On error, return -errno. + */ +static int open_file_handle(struct lo_data *lo, const struct lo_fhandle *fh, + int flags) +{ + struct lo_mount_fd *mfd; + int ret; + + ret = pthread_rwlock_rdlock(&lo->mount_fds_lock); + if (ret) { + return -ret; + } + + mfd = g_hash_table_lookup(lo->mount_fds, GINT_TO_POINTER(fh->mount_id)); + pthread_rwlock_unlock(&lo->mount_fds_lock); + if (!mfd) { + return -EINVAL; + } + + ret = open_by_handle_at(mfd->fd, (struct file_handle *)&fh->handle, flags); + if (ret < 0) { + return -errno; + } + + return ret; +} + /* * Load capng's state from our saved state if the current thread * hadn't previously been loaded. @@ -622,7 +736,10 @@ static void lo_inode_put(struct lo_data *lo, struct lo_inode **inodep) *inodep = NULL; if (g_atomic_int_dec_and_test(&inode->refcount)) { - close(inode->fd); + if (inode->fd >= 0) { + close(inode->fd); + } + release_file_handle(lo, inode->fhandle, true); free(inode); } } @@ -650,10 +767,25 @@ static struct lo_inode *lo_inode(fuse_req_t req, fuse_ino_t ino) static int lo_inode_fd(struct lo_data *lo, const struct lo_inode *inode, TempFd *tfd) { - *tfd = (TempFd) { - .fd = inode->fd, - .owned = false, - }; + if (inode->fd >= 0) { + *tfd = (TempFd) { + .fd = inode->fd, + .owned = false, + }; + } else { + int fd; + + assert(inode->fhandle != NULL); + fd = open_file_handle(lo, inode->fhandle, O_PATH); + if (fd < 0) { + return -errno; + } + + *tfd = (TempFd) { + .fd = fd, + .owned = true, + }; + } return 0; } @@ -694,22 +826,32 @@ static int lo_fd(fuse_req_t req, fuse_ino_t ino, TempFd *tfd) static int lo_inode_open(struct lo_data *lo, struct lo_inode *inode, int open_flags, TempFd *tfd) { - g_autofree char *fd_str = g_strdup_printf("%d", inode->fd); + g_autofree char *fd_str = NULL; int fd; if (!S_ISREG(inode->filetype) && !S_ISDIR(inode->filetype)) { return -EBADF; } - /* - * The file is a symlink so O_NOFOLLOW must be ignored. We checked earlier - * that the inode is not a special file but if an external process races - * with us then symlinks are traversed here. It is not possible to escape - * the shared directory since it is mounted as "/" though. - */ - fd = openat(lo->proc_self_fd, fd_str, open_flags & ~O_NOFOLLOW); - if (fd < 0) { - return -errno; + if (inode->fd >= 0) { + /* + * The file is a symlink so O_NOFOLLOW must be ignored. We checked + * earlier that the inode is not a special file but if an external + * process races with us then symlinks are traversed here. It is not + * possible to escape the shared directory since it is mounted as "/" + * though. + */ + fd_str = g_strdup_printf("%d", inode->fd); + fd = openat(lo->proc_self_fd, fd_str, open_flags & ~O_NOFOLLOW); + if (fd < 0) { + return -errno; + } + } else { + assert(inode->fhandle != NULL); + fd = open_file_handle(lo, inode->fhandle, open_flags); + if (fd < 0) { + return fd; + } } *tfd = (TempFd) { @@ -4187,6 +4329,9 @@ int main(int argc, char *argv[]) lo.root.fuse_ino = FUSE_ROOT_ID; lo.cache = CACHE_AUTO; + pthread_rwlock_init(&lo.mount_fds_lock, NULL); + lo.mount_fds = g_hash_table_new_full(NULL, NULL, NULL, free_lo_mount_fd); + /* * Set up the ino map like this: * [0] Reserved (will not be used) diff --git a/tools/virtiofsd/passthrough_seccomp.c b/tools/virtiofsd/passthrough_seccomp.c index f49ed94b5e..af04c638cb 100644 --- a/tools/virtiofsd/passthrough_seccomp.c +++ b/tools/virtiofsd/passthrough_seccomp.c @@ -77,6 +77,7 @@ static const int syscall_allowlist[] = { SCMP_SYS(statx), SCMP_SYS(open), SCMP_SYS(openat), + SCMP_SYS(open_by_handle_at), SCMP_SYS(ppoll), SCMP_SYS(prctl), /* TODO restrict to just PR_SET_NAME? */ SCMP_SYS(preadv), -- 2.31.1