| Message ID | 20210730150134.216126-8-mreitz@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | virtiofsd: Allow using file handles instead of O_PATH FDs | expand |
On Fri, Jul 30, 2021 at 05:01:31PM +0200, Max Reitz wrote: > 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 <mreitz@redhat.com> > Reviewed-by: Connor Kuehl <ckuehl@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 292b7f7e27..487448d666 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; > + How about if we move this hash table inside "struct lo_data". That seems to be one global data structure keeping all the info. Also it can be cleaned up during lo_destroy(). Thanks Vivek
On 09.08.21 17:21, Vivek Goyal wrote: > On Fri, Jul 30, 2021 at 05:01:31PM +0200, Max Reitz wrote: >> 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 <mreitz@redhat.com> >> Reviewed-by: Connor Kuehl <ckuehl@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 292b7f7e27..487448d666 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; >> + > How about if we move this hash table inside "struct lo_data". That seems to > be one global data structure keeping all the info. Also it can be > cleaned up during lo_destroy(). Yes, sounds good and right, will do. Hanna
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 292b7f7e27..487448d666 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 @@ -302,6 +319,44 @@ 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. @@ -608,7 +663,11 @@ 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); } } @@ -635,10 +694,25 @@ 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; } @@ -678,22 +752,32 @@ 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) { @@ -4110,6 +4194,8 @@ 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 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),