From: Zheng Liang <zhengliang6@xxxxxxxxxx>
From: Zheng Liang <zhengliang6@xxxxxxxxxx>
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 <zhengliang6@xxxxxxxxxx>
Fixes: e9be9d5e76e3 ("overlay filesystem")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.18
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Reference: CVE-2021-20321
Signed-off-by: Masami Ichikawa(CIP) <masami.ichikawa@xxxxxxxxxxxxxxxx>
---
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
