On Thu, Sep 16, 2021 at 10:40:35AM +0200, Hanna Reitz wrote:
> We only need to drop/switch our credentials for the (f)setxattr() call
> alone, not for the openat() or fchdir() around it.
>
> (Right now, this may not be that big of a problem, but with inodes being
> identified by file handles instead of an O_PATH fd, we will need
> open_by_handle_at() calls here, which is really fickle when it comes to
> credentials being dropped.)
>
> Signed-off-by: Hanna Reitz <hre...@redhat.com>
> ---
> tools/virtiofsd/passthrough_ll.c | 34 +++++++++++++++++++++++---------
> 1 file changed, 25 insertions(+), 9 deletions(-)
>
> diff --git a/tools/virtiofsd/passthrough_ll.c
> b/tools/virtiofsd/passthrough_ll.c
> index 6511a6acb4..b43afdfbd3 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -3123,6 +3123,7 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino,
> const char *in_name,
> bool switched_creds = false;
> bool cap_fsetid_dropped = false;
> struct lo_cred old = {};
> + bool changed_cwd = false;
>
> if (block_xattr(lo, in_name)) {
> fuse_reply_err(req, EOPNOTSUPP);
> @@ -3158,6 +3159,24 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t
> ino, const char *in_name,
> ", name=%s value=%s size=%zd)\n", ino, name, value, size);
>
> sprintf(procname, "%i", inode->fd);
> + /*
> + * We can only open regular files or directories. If the inode is
> + * something else, we have to enter /proc/self/fd and use
> + * setxattr() on the link's filename there.
> + */
> + if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) {
> + fd = openat(lo->proc_self_fd, procname, O_RDONLY);
> + if (fd < 0) {
> + saverr = errno;
> + goto out;
> + }
> + } else {
> + /* fchdir should not fail here */
> + FCHDIR_NOFAIL(lo->proc_self_fd);
> + /* Set flag so the clean-up path will chdir back */
> + changed_cwd = true;
Is there a need to move FCHDIR_NOFAIL() call earlier too? I am assuming
this will not be impacted by file handle stuff. So we probably could
leave it in place. Easier to read.
Vivek
> + }
> +
> /*
> * If we are setting posix access acl and if SGID needs to be
> * cleared, then switch to caller's gid and drop CAP_FSETID
> @@ -3178,20 +3197,12 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t
> ino, const char *in_name,
> }
> switched_creds = true;
> }
> - if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) {
> - fd = openat(lo->proc_self_fd, procname, O_RDONLY);
> - if (fd < 0) {
> - saverr = errno;
> - goto out;
> - }
> + if (fd >= 0) {
> ret = fsetxattr(fd, name, value, size, flags);
> saverr = ret == -1 ? errno : 0;
> } else {
> - /* fchdir should not fail here */
> - FCHDIR_NOFAIL(lo->proc_self_fd);
> ret = setxattr(procname, name, value, size, flags);
> saverr = ret == -1 ? errno : 0;
> - FCHDIR_NOFAIL(lo->root.fd);
> }
> if (switched_creds) {
> if (cap_fsetid_dropped)
> @@ -3201,6 +3212,11 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t
> ino, const char *in_name,
> }
>
> out:
> + if (changed_cwd) {
> + /* Change CWD back, fchdir should not fail here */
> + FCHDIR_NOFAIL(lo->root.fd);
> + }
> +
> if (fd >= 0) {
> close(fd);
> }
> --
> 2.31.1
>
