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.
Signed-off-by: Max Reitz <mre...@redhat.com>
Reviewed-by: Connor Kuehl <cku...@redhat.com>
---
tools/virtiofsd/passthrough_ll.c | 116 ++++++++++++++++++++++----
tools/virtiofsd/passthrough_seccomp.c | 1 +
2 files changed, 102 insertions(+), 15 deletions(-)
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 3014e8baf8..e665575401 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -88,8 +88,25 @@ 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;
+};
+
+/* Maps mount IDs to an FD that we can pass to open_by_handle_at() */
+static GHashTable *mount_fds;
+pthread_rwlock_t mount_fds_lock = PTHREAD_RWLOCK_INITIALIZER;
+
struct lo_inode {
+ /*
+ * Either of 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
@@ -296,6 +313,44 @@ static int temp_fd_steal(TempFd *temp_fd)
}
}
+/**
+ * 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(const struct lo_fhandle *fh, int flags)
+{
+ gpointer mount_fd_ptr;
+ int mount_fd;
+ bool found;
+ int ret;
+
+ ret = pthread_rwlock_rdlock(&mount_fds_lock);
+ if (ret) {
+ return -ret;
+ }
+
+ /* mount_fd == 0 is valid, so we need lookup_extended */
+ found = g_hash_table_lookup_extended(mount_fds,
+ GINT_TO_POINTER(fh->mount_id),
+ NULL, &mount_fd_ptr);
+ pthread_rwlock_unlock(&mount_fds_lock);
+ if (!found) {
+ return -EINVAL;
+ }
+ mount_fd = GPOINTER_TO_INT(mount_fd_ptr);
+
+ ret = open_by_handle_at(mount_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.
@@ -602,7 +657,11 @@ 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);
+ } else {
+ g_free(inode->fhandle);
+ }
free(inode);
}
}
@@ -629,10 +688,25 @@ static struct lo_inode *lo_inode(fuse_req_t req,
fuse_ino_t ino)
static int lo_inode_fd(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(inode->fhandle, O_PATH);
+ if (fd < 0) {
+ return -errno;
+ }
+
+ *tfd = (TempFd) {
+ .fd = fd,
+ .owned = true,
+ };
+ }
return 0;
}
@@ -672,22 +746,32 @@ static int lo_fd(fuse_req_t req, fuse_ino_t ino, TempFd
*tfd)
static int lo_inode_open(const struct lo_data *lo, const 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(inode->fhandle, open_flags);
+ if (fd < 0) {
+ return fd;
+ }
}
*tfd = (TempFd) {
@@ -3911,6 +3995,8 @@ int main(int argc, char *argv[])
lo.root.fuse_ino = FUSE_ROOT_ID;
lo.cache = CACHE_AUTO;
+ mount_fds = g_hash_table_new(NULL, NULL);
+
/*
* 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 62441cfcdb..e948f25ac1 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
