[Virtio-fs] [PATCH v4 3/3] virtiofsd: prevent opening of special files (CVE-2020-35517)
Vivek Goyal
vgoyal at redhat.com
Wed Feb 3 15:28:50 UTC 2021
On Wed, Feb 03, 2021 at 11:37:19AM +0000, Stefan Hajnoczi wrote:
[..]
> @@ -1727,36 +1764,38 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,
>
> update_open_flags(lo->writeback, lo->allow_direct_io, fi);
>
> - fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,
> - mode);
> + /* 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);
> err = fd == -1 ? errno : 0;
> +
> lo_restore_cred(&old);
>
> - if (!err) {
> - ssize_t fh;
> -
> - pthread_mutex_lock(&lo->mutex);
> - fh = lo_add_fd_mapping(lo, fd);
> - pthread_mutex_unlock(&lo->mutex);
> - if (fh == -1) {
> - close(fd);
> - err = ENOMEM;
> - goto out;
> - }
> + /* Ignore the error if file exists and O_EXCL was not given */
> + if (err && !(err == EEXIST && !(fi->flags & O_EXCL))) {
Can this check be simplified to.
if (err && (err == EEXIST && (fi->flags & O_EXCL)) {
goto out;
}
> + goto out;
> + }
Vivek
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