* Max Reitz (mre...@redhat.com) wrote:
> When the inode_file_handles option is set, try to generate a file handle
> for new inodes instead of opening an O_PATH FD.
>
> Being able to open these again will require CAP_DAC_READ_SEARCH, so the
> description text tells the user they will also need to specify
> -o modcaps=+dac_read_search.
>
> Generating a file handle returns the mount ID it is valid for. Opening
> it will require an FD instead. We have mount_fds to map an ID to an FD.
> get_file_handle() fills the hash map by opening the file we have
> generated a handle for. To verify that the resulting FD indeed
> represents the handle's mount ID, we use statx(). Therefore, using file
> handles requires statx() support.
>
> Signed-off-by: Max Reitz <mre...@redhat.com>
> ---
> tools/virtiofsd/helper.c | 3 +
> tools/virtiofsd/passthrough_ll.c | 170 ++++++++++++++++++++++++--
> tools/virtiofsd/passthrough_seccomp.c | 1 +
> 3 files changed, 165 insertions(+), 9 deletions(-)
>
> diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
> index 5e98ed702b..954f8639e6 100644
> --- a/tools/virtiofsd/helper.c
> +++ b/tools/virtiofsd/helper.c
> @@ -186,6 +186,9 @@ void fuse_cmdline_help(void)
> " to virtiofsd from guest
> applications.\n"
> " default: no_allow_direct_io\n"
> " -o announce_submounts Announce sub-mount points to the
> guest\n"
> + " -o inode_file_handles Use file handles to reference
> inodes\n"
> + " instead of O_PATH file
> descriptors\n"
> + " (requires -o
> modcaps=+dac_read_search)\n"
> );
> }
>
> diff --git a/tools/virtiofsd/passthrough_ll.c
> b/tools/virtiofsd/passthrough_ll.c
> index 793d2c333e..d01f9d3a59 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -190,6 +190,7 @@ struct lo_data {
> /* An O_PATH file descriptor to /proc/self/fd/ */
> int proc_self_fd;
> int user_killpriv_v2, killpriv_v2;
> + int inode_file_handles;
> };
>
> /**
> @@ -244,6 +245,10 @@ static const struct fuse_opt lo_opts[] = {
> { "announce_submounts", offsetof(struct lo_data, announce_submounts), 1
> },
> { "killpriv_v2", offsetof(struct lo_data, user_killpriv_v2), 1 },
> { "no_killpriv_v2", offsetof(struct lo_data, user_killpriv_v2), 0 },
> + { "inode_file_handles", offsetof(struct lo_data, inode_file_handles), 1
> },
> + { "no_inode_file_handles",
> + offsetof(struct lo_data, inode_file_handles),
> + 0 },
> FUSE_OPT_END
> };
> static bool use_syslog = false;
> @@ -315,6 +320,108 @@ static int temp_fd_steal(TempFd *temp_fd)
> }
> }
>
> +/**
> + * Generate a file handle for the given dirfd/name combination.
> + *
> + * If mount_fds does not yet contain an entry for the handle's mount
> + * ID, (re)open dirfd/name in O_RDONLY mode and add it to mount_fds
> + * as the FD for that mount ID. (That is the file that we have
> + * generated a handle for, so it should be representative for the
> + * mount ID. However, to be sure (and to rule out races), we use
> + * statx() to verify that our assumption is correct.)
> + */
> +static struct lo_fhandle *get_file_handle(struct lo_data *lo,
> + int dirfd, const char *name)
> +{
> + /* We need statx() to verify the mount ID */
> +#if defined(CONFIG_STATX) && defined(STATX_MNT_ID)
> + struct lo_fhandle *fh;
> + int ret;
> +
> + if (!lo->use_statx || !lo->inode_file_handles) {
> + return NULL;
> + }
> +
> + fh = g_new0(struct lo_fhandle, 1);
> +
> + fh->handle.handle_bytes = sizeof(fh->padding) - sizeof(fh->handle);
> + ret = name_to_handle_at(dirfd, name, &fh->handle, &fh->mount_id,
> + AT_EMPTY_PATH);
> + if (ret < 0) {
> + goto fail;
> + }
> +
> + if (pthread_rwlock_rdlock(&mount_fds_lock)) {
> + goto fail;
> + }
> + if (!g_hash_table_contains(mount_fds, GINT_TO_POINTER(fh->mount_id))) {
> + struct statx stx;
> + int fd;
> +
> + pthread_rwlock_unlock(&mount_fds_lock);
> +
> + if (name[0]) {
> + fd = openat(dirfd, name, O_RDONLY);
But can't that be a device file or other special file that you must not
open?
Dave
> + } else {
> + char procname[64];
> + snprintf(procname, sizeof(procname), "%i", dirfd);
> + fd = openat(lo->proc_self_fd, procname, O_RDONLY);
> + }
> + if (fd < 0) {
> + goto fail;
> + }
> +
> + ret = statx(fd, "", AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW,
> + STATX_MNT_ID, &stx);
> + if (ret < 0) {
> + if (errno == ENOSYS) {
> + lo->use_statx = false;
> + fuse_log(FUSE_LOG_WARNING,
> + "statx() does not work: Will not be able to use
> file "
> + "handles for inodes\n");
> + }
> + goto fail;
> + }
> + if (!(stx.stx_mask & STATX_MNT_ID) || stx.stx_mnt_id !=
> fh->mount_id) {
> + /*
> + * One reason for stx_mnt_id != mount_id could be that dirfd/name
> + * is a directory, and some other filesystem was mounted there
> + * between us generating the file handle and then opening the FD.
> + * (Other kinds of races might be possible, too.)
> + * Failing this function is not fatal, though, because our caller
> + * (lo_do_lookup()) will just fall back to opening an O_PATH FD
> to
> + * store in lo_inode.fd instead of storing a file handle in
> + * lo_inode.fhandle. So we do not need to try too hard to get an
> + * FD for fh->mount_id so this function could succeed.
> + */
> + goto fail;
> + }
> +
> + if (pthread_rwlock_wrlock(&mount_fds_lock)) {
> + goto fail;
> + }
> +
> + /* Check again, might have changed */
> + if (g_hash_table_contains(mount_fds, GINT_TO_POINTER(fh->mount_id)))
> {
> + close(fd);
> + } else {
> + g_hash_table_insert(mount_fds,
> + GINT_TO_POINTER(fh->mount_id),
> + GINT_TO_POINTER(fd));
> + }
> + }
> + pthread_rwlock_unlock(&mount_fds_lock);
> +
> + return fh;
> +
> +fail:
> + free(fh);
> + return NULL;
> +#else /* defined(CONFIG_STATX) && defined(STATX_MNT_ID) */
> + return NULL;
> +#endif
> +}
> +
> /**
> * Open the given file handle with the given flags.
> *
> @@ -1132,6 +1239,11 @@ static int do_statx(struct lo_data *lo, int dirfd,
> const char *pathname,
> return -1;
> }
> lo->use_statx = false;
> + if (lo->inode_file_handles) {
> + fuse_log(FUSE_LOG_WARNING,
> + "statx() does not work: Will not be able to use file "
> + "handles for inodes\n");
> + }
> /* fallback */
> }
> #endif
> @@ -1161,6 +1273,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t
> parent, const char *name,
> struct lo_data *lo = lo_data(req);
> struct lo_inode *inode = NULL;
> struct lo_inode *dir = lo_inode(req, parent);
> + struct lo_fhandle *fh;
>
> if (inodep) {
> *inodep = NULL; /* in case there is an error */
> @@ -1190,13 +1303,19 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t
> parent, const char *name,
> goto out;
> }
>
> - newfd = openat(dir_fd.fd, name, O_PATH | O_NOFOLLOW);
> - if (newfd == -1) {
> - goto out_err;
> - }
> + fh = get_file_handle(lo, dir_fd.fd, name);
> + if (fh) {
> + res = do_statx(lo, dir_fd.fd, name, &e->attr,
> + AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW, &mnt_id);
> + } else {
> + newfd = openat(dir_fd.fd, name, O_PATH | O_NOFOLLOW);
> + if (newfd == -1) {
> + goto out_err;
> + }
>
> - res = do_statx(lo, newfd, "", &e->attr, AT_EMPTY_PATH |
> AT_SYMLINK_NOFOLLOW,
> - &mnt_id);
> + res = do_statx(lo, newfd, "", &e->attr,
> + AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW, &mnt_id);
> + }
> if (res == -1) {
> goto out_err;
> }
> @@ -1206,9 +1325,19 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t
> parent, const char *name,
> e->attr_flags |= FUSE_ATTR_SUBMOUNT;
> }
>
> - inode = lo_find(lo, NULL, &e->attr, mnt_id);
> + /*
> + * Note that fh is always NULL if lo->inode_file_handles is false,
> + * and so we will never do a lookup by file handle here, and
> + * lo->inodes_by_handle will always remain empty. We only need
> + * this map when we do not have an O_PATH fd open for every
> + * lo_inode, though, so if inode_file_handles is false, we do not
> + * need that map anyway.
> + */
> + inode = lo_find(lo, fh, &e->attr, mnt_id);
> if (inode) {
> - close(newfd);
> + if (newfd != -1) {
> + close(newfd);
> + }
> } else {
> inode = calloc(1, sizeof(struct lo_inode));
> if (!inode) {
> @@ -1226,6 +1355,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t
> parent, const char *name,
>
> inode->nlookup = 1;
> inode->fd = newfd;
> + inode->fhandle = fh;
> inode->key.ino = e->attr.st_ino;
> inode->key.dev = e->attr.st_dev;
> inode->key.mnt_id = mnt_id;
> @@ -1237,6 +1367,9 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t
> parent, const char *name,
> pthread_mutex_lock(&lo->mutex);
> inode->fuse_ino = lo_add_inode_mapping(req, inode);
> g_hash_table_insert(lo->inodes_by_ids, &inode->key, inode);
> + if (inode->fhandle) {
> + g_hash_table_insert(lo->inodes_by_handle, inode->fhandle, inode);
> + }
> pthread_mutex_unlock(&lo->mutex);
> }
> e->ino = inode->fuse_ino;
> @@ -1530,8 +1663,10 @@ static struct lo_inode *lookup_name(fuse_req_t req,
> fuse_ino_t parent,
> int res;
> uint64_t mnt_id;
> struct stat attr;
> + struct lo_fhandle *fh;
> struct lo_data *lo = lo_data(req);
> struct lo_inode *dir = lo_inode(req, parent);
> + struct lo_inode *inode;
>
> if (!dir) {
> return NULL;
> @@ -1542,13 +1677,19 @@ static struct lo_inode *lookup_name(fuse_req_t req,
> fuse_ino_t parent,
> return NULL;
> }
>
> + fh = get_file_handle(lo, dir_fd.fd, name);
> + /* Ignore errors, this is just an optional key for the lookup */
> +
> res = do_statx(lo, dir_fd.fd, name, &attr, AT_SYMLINK_NOFOLLOW, &mnt_id);
> lo_inode_put(lo, &dir);
> if (res == -1) {
> return NULL;
> }
>
> - return lo_find(lo, NULL, &attr, mnt_id);
> + inode = lo_find(lo, fh, &attr, mnt_id);
> + g_free(fh);
> +
> + return inode;
> }
>
> static void lo_rmdir(fuse_req_t req, fuse_ino_t parent, const char *name)
> @@ -1712,6 +1853,9 @@ static void unref_inode(struct lo_data *lo, struct
> lo_inode *inode, uint64_t n)
> if (!inode->nlookup) {
> lo_map_remove(&lo->ino_map, inode->fuse_ino);
> g_hash_table_remove(lo->inodes_by_ids, &inode->key);
> + if (inode->fhandle) {
> + g_hash_table_remove(lo->inodes_by_handle, inode->fhandle);
> + }
> if (lo->posix_lock) {
> if (g_hash_table_size(inode->posix_locks)) {
> fuse_log(FUSE_LOG_WARNING, "Hash table is not empty\n");
> @@ -4156,6 +4300,14 @@ int main(int argc, char *argv[])
>
> lo.use_statx = true;
>
> +#if !defined(CONFIG_STATX) || !defined(STATX_MNT_ID)
> + if (lo.inode_file_handles) {
> + fuse_log(FUSE_LOG_WARNING,
> + "No statx() or mount ID support: Will not be able to use
> file "
> + "handles for inodes\n");
> + }
> +#endif
> +
> se = fuse_session_new(&args, &lo_oper, sizeof(lo_oper), &lo);
> if (se == NULL) {
> goto err_out1;
> diff --git a/tools/virtiofsd/passthrough_seccomp.c
> b/tools/virtiofsd/passthrough_seccomp.c
> index e948f25ac1..ed23e67ba8 100644
> --- a/tools/virtiofsd/passthrough_seccomp.c
> +++ b/tools/virtiofsd/passthrough_seccomp.c
> @@ -73,6 +73,7 @@ static const int syscall_allowlist[] = {
> SCMP_SYS(mprotect),
> SCMP_SYS(mremap),
> SCMP_SYS(munmap),
> + SCMP_SYS(name_to_handle_at),
> SCMP_SYS(newfstatat),
> SCMP_SYS(statx),
> SCMP_SYS(open),
> --
> 2.31.1
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
