From: Zheng Liang zhengliang6@huawei.com
mainline inclusion from mainline-v5.15-rc5 commit a295aef603e109a47af355477326bd41151765b6 category: bugfix bugzilla: NA CVE: NA
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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@huawei.com Fixes: e9be9d5e76e3 ("overlay filesystem") Cc: stable@vger.kernel.org # v3.18 Signed-off-by: Miklos Szeredi mszeredi@redhat.com Reviewed-by: Zhang Yi yi.zhang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- 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 9902c1706be91..1de8ef95ad960 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -1188,9 +1188,13 @@ static int ovl_rename(struct inode *olddir, struct dentry *old, goto out_dput; } } else { - 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)