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ovl: fix use inode directly in rcu-walk mode 

ovl_dentry_revalidate_common() can be called in rcu-walk mode.  As document
said, "in rcu-walk mode, d_parent and d_inode should not be used without
care".

Check inode here to protect access under rcu-walk mode.

Fixes: bccece1ead ("ovl: allow remote upper")
Reported-and-tested-by: syzbot+a4055c78774bbf3498bb@syzkaller.appspotmail.com
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Cc: <stable@vger.kernel.org> # v5.7
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Chen Zhongjin 2022-11-28 11:33:05 +01:00 committed by Miklos Szeredi
parent eb7081409f
commit 672e4268b2
1 changed files with 6 additions and 1 deletions
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7
fs/overlayfs/super.c
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@ -139,11 +139,16 @@ static int ovl_dentry_revalidate_common(struct dentry *dentry,
unsigned int flags, bool weak)
{
struct ovl_entry *oe = dentry->d_fsdata;
struct inode *inode = d_inode_rcu(dentry);
struct dentry *upper;
unsigned int i;
int ret = 1;
upper = ovl_dentry_upper(dentry);
/* Careful in RCU mode */
if (!inode)
return -ECHILD;
upper = ovl_i_dentry_upper(inode);
if (upper)
ret = ovl_revalidate_real(upper, flags, weak);