* 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.
> ---
> 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:
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
