From 1e43a0933de1ab853f171de45a17b5f9c43b110e Mon Sep 17 00:00:00 2001 From: Zheng Liang Date: Fri, 24 Sep 2021 09:16:27 +0800 Subject: [PATCH] ovl: fix missing negative dentry check in ovl_rename() From: Zheng Liang commit a295aef603e109a47af355477326bd41151765b6 upstream. The following reproducer mkdir lower upper work merge touch lower/old touch lower/new mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merge rm merge/new mv merge/old merge/new & unlink upper/new may result in this race: PROCESS A: rename("merge/old", "merge/new"); overwrite=true,ovl_lower_positive(old)=true, ovl_dentry_is_whiteout(new)=true -> flags |= RENAME_EXCHANGE PROCESS B: unlink("upper/new"); PROCESS A: lookup newdentry in new_upperdir call vfs_rename() with negative newdentry and RENAME_EXCHANGE Fix by adding the missing check for negative newdentry. Signed-off-by: Zheng Liang Fixes: e9be9d5e76e3 ("overlay filesystem") Cc: # v3.18 Signed-off-by: Miklos Szeredi Reference: CVE-2021-20321 Signed-off-by: Masami Ichikawa(CIP) --- fs/overlayfs/dir.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index eedacae889b9..80bf0ab52e81 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -824,9 +824,13 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old, } } else { new_create = true; - if (!d_is_negative(newdentry) && - (!new_opaque || !ovl_is_whiteout(newdentry))) - goto out_dput; + if (!d_is_negative(newdentry)) { + if (!new_opaque || !ovl_is_whiteout(newdentry)) + goto out_dput; + } else { + if (flags & RENAME_EXCHANGE) + goto out_dput; + } } if (olddentry == trap) -- 2.33.0