From 20396365a16dae4b4e3967fc7115d5336feb30ee Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Sun, 21 Jun 2020 09:37:59 +0300 Subject: ovl: fix oops in ovl_indexdir_cleanup() with nfs_export=on Mounting with nfs_export=on, xfstests overlay/031 triggers a kernel panic since v5.8-rc1 overlayfs updates. overlayfs: orphan index entry (index/00fb1..., ftype=4000, nlink=2) BUG: kernel NULL pointer dereference, address: 0000000000000030 RIP: 0010:ovl_cleanup_and_whiteout+0x28/0x220 [overlay] Bisect point at commit c21c839b8448 ("ovl: whiteout inode sharing") Minimal reproducer: -------------------------------------------------- rm -rf l u w m mkdir -p l u w m mkdir -p l/testdir touch l/testdir/testfile mount -t overlay -o lowerdir=l,upperdir=u,workdir=w,nfs_export=on overlay m echo 1 > m/testdir/testfile umount m rm -rf u/testdir mount -t overlay -o lowerdir=l,upperdir=u,workdir=w,nfs_export=on overlay m umount m -------------------------------------------------- When mount with nfs_export=on, and fail to verify an orphan index, we're cleaning this index from indexdir by calling ovl_cleanup_and_whiteout(). This dereferences ofs->workdir, that was earlier set to NULL. The design was that ovl->workdir will point at ovl->indexdir, but we are assigning ofs->indexdir to ofs->workdir only after ovl_indexdir_cleanup(). There is no reason not to do it sooner, because once we get success from ofs->indexdir = ovl_workdir_create(... there is no turning back. Reported-and-tested-by: Murphy Zhou Fixes: c21c839b8448 ("ovl: whiteout inode sharing") Signed-off-by: Amir Goldstein Signed-off-by: Miklos Szeredi --- fs/overlayfs/super.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-) (limited to 'fs') diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 498d49d5dd19..31ef24dfcf88 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1354,6 +1354,12 @@ static int ovl_get_indexdir(struct super_block *sb, struct ovl_fs *ofs, ofs->indexdir = ovl_workdir_create(ofs, OVL_INDEXDIR_NAME, true); if (ofs->indexdir) { + /* index dir will act also as workdir */ + iput(ofs->workdir_trap); + ofs->workdir_trap = NULL; + dput(ofs->workdir); + ofs->workdir = dget(ofs->indexdir); + err = ovl_setup_trap(sb, ofs->indexdir, &ofs->indexdir_trap, "indexdir"); if (err) @@ -1852,20 +1858,12 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) sb->s_flags |= SB_RDONLY; if (!(ovl_force_readonly(ofs)) && ofs->config.index) { - /* index dir will act also as workdir */ - dput(ofs->workdir); - ofs->workdir = NULL; - iput(ofs->workdir_trap); - ofs->workdir_trap = NULL; - err = ovl_get_indexdir(sb, ofs, oe, &upperpath); if (err) goto out_free_oe; /* Force r/o mount with no index dir */ - if (ofs->indexdir) - ofs->workdir = dget(ofs->indexdir); - else + if (!ofs->indexdir) sb->s_flags |= SB_RDONLY; } -- cgit v1.2.3