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 | 194 ++++++++++++++++++++++++--
tools/virtiofsd/passthrough_seccomp.c | 1 +
3 files changed, 190 insertions(+), 8 deletions(-)
diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
index a8295d975a..aa63a21d43 100644
--- a/tools/virtiofsd/helper.c
+++ b/tools/virtiofsd/helper.c
@@ -187,6 +187,9 @@ void fuse_cmdline_help(void)
" default: no_allow_direct_io\n"
" -o announce_submounts Announce sub-mount points to the
guest\n"
" -o posix_acl/no_posix_acl Enable/Disable posix_acl. (default:
disabled)\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 f9d8b2f134..ac95961d12 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -194,6 +194,7 @@ struct lo_data {
/* If set, virtiofsd is responsible for setting umask during creation */
bool change_umask;
int user_posix_acl, posix_acl;
+ int inode_file_handles;
};
/**
@@ -250,6 +251,10 @@ static const struct fuse_opt lo_opts[] = {
{ "no_killpriv_v2", offsetof(struct lo_data, user_killpriv_v2), 0 },
{ "posix_acl", offsetof(struct lo_data, user_posix_acl), 1 },
{ "no_posix_acl", offsetof(struct lo_data, user_posix_acl), 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;
@@ -321,6 +326,135 @@ 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))) {
+ g_auto(TempFd) path_fd = TEMP_FD_INIT;
+ struct statx stx;
+ char procname[64];
+ int fd;
+
+ pthread_rwlock_unlock(&mount_fds_lock);
+
+ /*
+ * Before opening an O_RDONLY fd, check whether dirfd/name is a regular
+ * file or directory, because we must not open anything else with
+ * anything but O_PATH.
+ * (And we use that occasion to verify that the file has the mount ID
we
+ * need.)
+ */
+ if (name[0]) {
+ path_fd.fd = openat(dirfd, name, O_PATH);
+ if (path_fd.fd < 0) {
+ goto fail;
+ }
+ path_fd.owned = true;
+ } else {
+ path_fd.fd = dirfd;
+ path_fd.owned = false;
+ }
+
+ ret = statx(path_fd.fd, "", AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW,
+ STATX_TYPE | 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 (!(stx.stx_mask & STATX_TYPE) ||
+ !(S_ISREG(stx.stx_mode) || S_ISDIR(stx.stx_mode)))
+ {
+ /*
+ * We must not open special files with anything but O_PATH, so we
+ * cannot use this file for mount_fds.
+ * Just return a failure in such a case and let the lo_inode have
+ * an O_PATH fd instead of a file handle.
+ */
+ goto fail;
+ }
+
+ /* Now that we know this fd is safe to open, do it */
+ snprintf(procname, sizeof(procname), "%i", path_fd.fd);
+ fd = openat(lo->proc_self_fd, procname, O_RDONLY);
+ if (fd < 0) {
+ 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.
*
@@ -1165,6 +1299,11 @@ 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
@@ -1194,6 +1333,7 @@ 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 */
@@ -1223,13 +1363,21 @@ 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) {
+ 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);
+ if (newfd >= 0) {
+ res = do_statx(lo, newfd, "", &e->attr,
+ AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW, &mnt_id);
+ } else {
+ res = do_statx(lo, dir_fd.fd, name, &e->attr,
+ AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW, &mnt_id);
+ }
if (res == -1) {
goto out_err;
}
@@ -1239,9 +1387,19 @@ 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) {
@@ -1259,6 +1417,7 @@ 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;
@@ -1270,6 +1429,9 @@ 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;
@@ -1615,6 +1777,7 @@ 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 = NULL;
@@ -1628,12 +1791,16 @@ static struct lo_inode *lookup_name(fuse_req_t req,
fuse_ino_t parent,
goto out;
}
+ 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);
if (res == -1) {
goto out;
}
- inode = lo_find(lo, NULL, &attr, mnt_id);
+ inode = lo_find(lo, fh, &attr, mnt_id);
+ g_free(fh);
out:
lo_inode_put(lo, &dir);
@@ -1801,6 +1968,9 @@ 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");
@@ -4362,6 +4532,14 @@ 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 af04c638cb..ab4dc07e3f 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
