On Mon, Feb 07, 2022 at 11:38:12AM +0000, Dr. David Alan Gilbert wrote: > * Vivek Goyal (vgo...@redhat.com) wrote: > > This patch adds support to set /proc/thread-self/attr/fscreate before > > file creation. It is set to a value as sent by client. This will allow > > for atomic creation of security context on files w.r.t file creation. > > > > This is primarily useful when either there is no SELinux enabled on > > host or host and guest policies are in sync and don't conflict. > > > > Signed-off-by: Vivek Goyal <vgo...@redhat.com> > > Minor nit below, but I think this is right: > > Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > > I would however prefer if you could split this patch; it's a bit long to > review.
Ok, I will look into splitting it. > > > > --- > > tools/virtiofsd/passthrough_ll.c | 317 ++++++++++++++++++++++++++++--- > > 1 file changed, 290 insertions(+), 27 deletions(-) > > > > diff --git a/tools/virtiofsd/passthrough_ll.c > > b/tools/virtiofsd/passthrough_ll.c > > index 82023bf3d4..acb99aa2fc 100644 > > --- a/tools/virtiofsd/passthrough_ll.c > > +++ b/tools/virtiofsd/passthrough_ll.c > > @@ -173,10 +173,14 @@ struct lo_data { > > > > /* An O_PATH file descriptor to /proc/self/fd/ */ > > int proc_self_fd; > > + /* An O_PATH file descriptor to /proc/self/task/ */ > > + int proc_self_task; > > int user_killpriv_v2, killpriv_v2; > > /* If set, virtiofsd is responsible for setting umask during creation > > */ > > bool change_umask; > > int user_posix_acl, posix_acl; > > + /* Keeps track if /proc/<pid>/attr/fscreate should be used or not */ > > + bool use_fscreate; > > }; > > > > static const struct fuse_opt lo_opts[] = { > > @@ -230,6 +234,11 @@ static struct lo_inode *lo_find(struct lo_data *lo, > > struct stat *st, > > static int xattr_map_client(const struct lo_data *lo, const char > > *client_name, > > char **out_name); > > > > +#define FCHDIR_NOFAIL(fd) do { \ > > + int fchdir_res = fchdir(fd); \ > > + assert(fchdir_res == 0); \ > > + } while (0) > > + > > static bool is_dot_or_dotdot(const char *name) > > { > > return name[0] == '.' && > > @@ -256,6 +265,33 @@ static struct lo_data *lo_data(fuse_req_t req) > > return (struct lo_data *)fuse_req_userdata(req); > > } > > > > +/* > > + * Tries to figure out if /proc/<pid>/attr/fscrate is usable or not. With > > + * selinux=0, read from fscreate returns -EINVAL. > > + * > > + * TODO: Link with libselinux and use is_selinux_enabled() instead down > > + * the line. It probably will be more reliable indicator. > > + */ > > +static bool is_fscreate_usable(struct lo_data *lo) > > +{ > > + char procname[64]; > > + int fscreate_fd; > > + size_t bytes_read; > > + > > + sprintf(procname, "%d/attr/fscreate", gettid()); > > + fscreate_fd = openat(lo->proc_self_task, procname, O_RDWR); > > + if (fscreate_fd == -1) { > > + return false; > > + } > > + > > + bytes_read = read(fscreate_fd, procname, 64); > > + close(fscreate_fd); > > + if (bytes_read == -1) { > > + return false; > > + } > > + return true; > > +} > > + > > /* > > * Load capng's state from our saved state if the current thread > > * hadn't previously been loaded. > > @@ -1284,16 +1320,140 @@ static void lo_restore_cred_gain_cap(struct > > lo_cred *old, bool restore_umask, > > } > > } > > > > +/* Helpers to set/reset fscreate */ > > +static int open_set_proc_fscreate(struct lo_data *lo, const void *ctx, > > + size_t ctxlen, int *fd) > > +{ > > + char procname[64]; > > + int fscreate_fd, err = 0; > > + size_t written; > > + > > + sprintf(procname, "%d/attr/fscreate", gettid()); > > + fscreate_fd = openat(lo->proc_self_task, procname, O_WRONLY); > > + err = fscreate_fd == -1 ? errno : 0; > > + if (err) { > > + return err; > > + } > > + > > + written = write(fscreate_fd, ctx, ctxlen); > > + err = written == -1 ? errno : 0; > > + if (err) { > > + goto out; > > + } > > + > > + *fd = fscreate_fd; > > + return 0; > > +out: > > + close(fscreate_fd); > > + return err; > > +} > > + > > +static void close_reset_proc_fscreate(int fd) > > +{ > > + if ((write(fd, NULL, 0)) == -1) { > > + fuse_log(FUSE_LOG_WARNING, "Failed to reset fscreate. err=%d\n", > > errno); > > + } > > + close(fd); > > + return; > > +} > > + > > +static int do_mknod_symlink_secctx(fuse_req_t req, struct lo_inode *dir, > > + const char *name, const char > > *secctx_name) > > +{ > > + int path_fd, err; > > + char procname[64]; > > + struct lo_data *lo = lo_data(req); > > + > > + if (!req->secctx.ctxlen) { > > + return 0; > > + } > > + > > + /* Open newly created element with O_PATH */ > > + path_fd = openat(dir->fd, name, O_PATH | O_NOFOLLOW); > > + err = path_fd == -1 ? errno : 0; > > + if (err) { > > + return err; > > + } > > + sprintf(procname, "%i", path_fd); > > + FCHDIR_NOFAIL(lo->proc_self_fd); > > + /* Set security context. This is not atomic w.r.t file creation */ > > + err = setxattr(procname, secctx_name, req->secctx.ctx, > > req->secctx.ctxlen, > > + 0); > > + if (err) { > > + err = errno; > > + } > > + FCHDIR_NOFAIL(lo->root.fd); > > + close(path_fd); > > + return err; > > +} > > + > > +static int do_mknod_symlink(fuse_req_t req, struct lo_inode *dir, > > + const char *name, mode_t mode, dev_t rdev, > > + const char *link) > > +{ > > + int err, fscreate_fd = -1; > > + const char *secctx_name = req->secctx.name; > > + struct lo_cred old = {}; > > + struct lo_data *lo = lo_data(req); > > + char *mapped_name = NULL; > > + bool secctx_enabled = req->secctx.ctxlen; > > + bool do_fscreate = false; > > + > > + if (secctx_enabled && lo->xattrmap) { > > + err = xattr_map_client(lo, req->secctx.name, &mapped_name); > > + if (err < 0) { > > + return -err; > > + } > > + secctx_name = mapped_name; > > + } > > + > > + /* > > + * If security xattr has not been remapped and selinux is enabled on > > + * host, set fscreate and no need to do a setxattr() after file > > creation > > + */ > > + if (secctx_enabled && !mapped_name && lo->use_fscreate) { > > + do_fscreate = true; > > + err = open_set_proc_fscreate(lo, req->secctx.ctx, > > req->secctx.ctxlen, > > + &fscreate_fd); > > + if (err) { > > + goto out; > > + } > > + } > > + > > + err = lo_change_cred(req, &old, lo->change_umask && !S_ISLNK(mode)); > > + if (err) { > > + goto out; > > + } > > + > > + err = mknod_wrapper(dir->fd, name, link, mode, rdev); > > + err = err == -1 ? errno : 0; > > + lo_restore_cred(&old, lo->change_umask && !S_ISLNK(mode)); > > + if (err) { > > + goto out; > > + } > > + > > + if (!do_fscreate) { > > + err = do_mknod_symlink_secctx(req, dir, name, secctx_name); > > + if (err) { > > + unlinkat(dir->fd, name, S_ISDIR(mode) ? AT_REMOVEDIR : 0); > > + } > > + } > > +out: > > + if (fscreate_fd != -1) { > > + close_reset_proc_fscreate(fscreate_fd); > > + } > > + g_free(mapped_name); > > + return err; > > +} > > + > > static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t parent, > > const char *name, mode_t mode, dev_t rdev, > > const char *link) > > { > > - int res; > > int saverr; > > struct lo_data *lo = lo_data(req); > > struct lo_inode *dir; > > struct fuse_entry_param e; > > - struct lo_cred old = {}; > > > > if (is_empty(name)) { > > fuse_reply_err(req, ENOENT); > > @@ -1311,21 +1471,11 @@ static void lo_mknod_symlink(fuse_req_t req, > > fuse_ino_t parent, > > return; > > } > > > > - saverr = lo_change_cred(req, &old, lo->change_umask && !S_ISLNK(mode)); > > + saverr = do_mknod_symlink(req, dir, name, mode, rdev, link); > > if (saverr) { > > goto out; > > } > > > > - res = mknod_wrapper(dir->fd, name, link, mode, rdev); > > - > > - saverr = errno; > > - > > - lo_restore_cred(&old, lo->change_umask && !S_ISLNK(mode)); > > - > > - if (res == -1) { > > - goto out; > > - } > > - > > saverr = lo_do_lookup(req, parent, name, &e, NULL); > > if (saverr) { > > goto out; > > @@ -2001,13 +2151,16 @@ static int lo_do_open(struct lo_data *lo, struct > > lo_inode *inode, > > return 0; > > } > > > > -static int do_lo_create(fuse_req_t req, struct lo_inode *parent_inode, > > - const char *name, mode_t mode, > > - struct fuse_file_info *fi, int* open_fd) > > +static int do_create_nosecctx(fuse_req_t req, struct lo_inode > > *parent_inode, > > + const char *name, mode_t mode, > > + struct fuse_file_info *fi, int *open_fd) > > { > > - int err = 0, fd; > > + int err, fd; > > struct lo_cred old = {}; > > struct lo_data *lo = lo_data(req); > > + int flags; > > + > > + flags = fi->flags | O_CREAT | O_EXCL; > > > > err = lo_change_cred(req, &old, lo->change_umask); > > if (err) { > > @@ -2015,13 +2168,106 @@ static int do_lo_create(fuse_req_t req, struct > > lo_inode *parent_inode, > > } > > > > /* Try to create a new file but don't open existing files */ > > - fd = openat(parent_inode->fd, name, fi->flags | O_CREAT | O_EXCL, > > mode); > > - if (fd == -1) { > > - err = errno; > > - } else { > > + fd = openat(parent_inode->fd, name, flags, mode); > > + err = fd == -1 ? errno : 0; > > + lo_restore_cred(&old, lo->change_umask); > > + if (!err) { > > *open_fd = fd; > > } > > - lo_restore_cred(&old, lo->change_umask); > > + return err; > > +} > > + > > +static int do_create_secctx_fscreate(fuse_req_t req, > > + struct lo_inode *parent_inode, > > + const char *name, mode_t mode, > > + struct fuse_file_info *fi, int > > *open_fd) > > +{ > > + int err = 0, fd = -1, fscreate_fd = -1; > > + struct lo_data *lo = lo_data(req); > > + > > + err = open_set_proc_fscreate(lo, req->secctx.ctx, req->secctx.ctxlen, > > + &fscreate_fd); > > + if (err) { > > + return err; > > + } > > + > > + err = do_create_nosecctx(req, parent_inode, name, mode, fi, &fd); > > + > > + close_reset_proc_fscreate(fscreate_fd); > > + if (!err) { > > + *open_fd = fd; > > + } > > + return err; > > +} > > + > > +static int do_create_secctx_noatomic(fuse_req_t req, > > + struct lo_inode *parent_inode, > > + const char *name, mode_t mode, > > + struct fuse_file_info *fi, > > + const char *secctx_name, int *open_fd) > > +{ > > + int err = 0, fd = -1; > > + > > + err = do_create_nosecctx(req, parent_inode, name, mode, fi, &fd); > > + if (err) { > > + goto out; > > + } > > + > > + /* Set security context. This is not atomic w.r.t file creation */ > > + err = fsetxattr(fd, secctx_name, req->secctx.ctx, req->secctx.ctxlen, > > 0); > > + err = err == -1 ? errno : 0; > > +out: > > + if (!err) { > > + *open_fd = fd; > > + } else { > > + if (fd != -1) { > > + close(fd); > > + unlinkat(parent_inode->fd, name, 0); > > + } > > + } > > + return err; > > +} > > + > > +static int do_lo_create(fuse_req_t req, struct lo_inode *parent_inode, > > + const char *name, mode_t mode, > > + struct fuse_file_info *fi, int *open_fd) > > +{ > > + struct lo_data *lo = lo_data(req); > > + char *mapped_name = NULL; > > + int err; > > + const char *ctxname = req->secctx.name; > > + bool secctx_enabled = req->secctx.ctxlen; > > + > > + if (secctx_enabled && lo->xattrmap) { > > + err = xattr_map_client(lo, req->secctx.name, &mapped_name); > > + if (err < 0) { > > + return -err; > > + } > > + > > + ctxname = mapped_name; > > + } > > + > > + if (secctx_enabled) { > > + /* > > + * If security.selinux has not been remapped and selinux is > > enabled, > > + * use fscreate to set context before file creation. > > + * Otherwise fallback to non-atomic method of file creation > > + * and xattr settting. > > + */ > > + if (!mapped_name && lo->use_fscreate) { > > + err = do_create_secctx_fscreate(req, parent_inode, name, mode, > > fi, > > + open_fd); > > + goto out; > > This can turn into another nested } else { and you don't need the out: > I guess I will have to put do_create_secctx_noatomic() into an else{} to get rid of "goto out". The downside is that in second else loop, I need to fallback non-atomic secctx creation. That means I will have to call do_create_secctx_noatomic() one more time inside second else block to fallback. I feel I like current structure better until and unless you strongly feel about it. Thanks Vivek > Dave > > + } > > + > > + err = do_create_secctx_noatomic(req, parent_inode, name, mode, fi, > > + ctxname, open_fd); > > + } else { > > + err = do_create_nosecctx(req, parent_inode, name, mode, fi, > > open_fd); > > + } > > + > > +out: > > + g_free(mapped_name); > > return err; > > } > > > > @@ -2856,11 +3102,6 @@ static int xattr_map_server(const struct lo_data > > *lo, const char *server_name, > > return -ENODATA; > > } > > > > -#define FCHDIR_NOFAIL(fd) do { \ > > - int fchdir_res = fchdir(fd); \ > > - assert(fchdir_res == 0); \ > > - } while (0) > > - > > static bool block_xattr(struct lo_data *lo, const char *name) > > { > > /* > > @@ -3522,6 +3763,15 @@ static void setup_namespaces(struct lo_data *lo, > > struct fuse_session *se) > > exit(1); > > } > > > > + /* Get the /proc/self/task descriptor */ > > + lo->proc_self_task = open("/proc/self/task/", O_PATH); > > + if (lo->proc_self_task == -1) { > > + fuse_log(FUSE_LOG_ERR, "open(/proc/self/task, O_PATH): %m\n"); > > + exit(1); > > + } > > + > > + lo->use_fscreate = is_fscreate_usable(lo); > > + > > /* > > * We only need /proc/self/fd. Prevent ".." from accessing parent > > * directories of /proc/self/fd by bind-mounting it over /proc. Since > > / was > > @@ -3738,6 +3988,14 @@ static void setup_chroot(struct lo_data *lo) > > exit(1); > > } > > > > + lo->proc_self_task = open("/proc/self/task", O_PATH); > > + if (lo->proc_self_fd == -1) { > > + fuse_log(FUSE_LOG_ERR, "open(\"/proc/self/task\", O_PATH): %m\n"); > > + exit(1); > > + } > > + > > + lo->use_fscreate = is_fscreate_usable(lo); > > + > > /* > > * Make the shared directory the file system root so that FUSE_OPEN > > * (lo_open()) cannot escape the shared directory by opening a symlink. > > @@ -3923,6 +4181,10 @@ static void fuse_lo_data_cleanup(struct lo_data *lo) > > close(lo->proc_self_fd); > > } > > > > + if (lo->proc_self_task >= 0) { > > + close(lo->proc_self_task); > > + } > > + > > if (lo->root.fd >= 0) { > > close(lo->root.fd); > > } > > @@ -3950,6 +4212,7 @@ int main(int argc, char *argv[]) > > .posix_lock = 0, > > .allow_direct_io = 0, > > .proc_self_fd = -1, > > + .proc_self_task = -1, > > .user_killpriv_v2 = -1, > > .user_posix_acl = -1, > > }; > > -- > > 2.34.1 > > > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK >