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: Max Reitz <mre...@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 38b2af8599..1f27eeabc5 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -3121,6 +3121,7 @@ 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 open_inode; if (block_xattr(lo, in_name)) { fuse_reply_err(req, EOPNOTSUPP); @@ -3155,7 +3156,24 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, fuse_log(FUSE_LOG_DEBUG, "lo_setxattr(ino=%" PRIu64 ", name=%s value=%s size=%zd)\n", ino, name, value, size); + /* + * 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. + */ + open_inode = S_ISREG(inode->filetype) || S_ISDIR(inode->filetype); sprintf(procname, "%i", inode->fd); + if (open_inode) { + 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); + } + /* * If we are setting posix access acl and if SGID needs to be * cleared, then switch to caller's gid and drop CAP_FSETID @@ -3176,20 +3194,13 @@ 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 (open_inode) { + assert(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) @@ -3198,6 +3209,11 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, lo_restore_cred(&old, false); } + if (!open_inode) { + /* Change CWD back, fchdir should not fail here */ + FCHDIR_NOFAIL(lo->root.fd); + } + out: if (fd >= 0) { close(fd); -- 2.31.1