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Message-ID: <20230515133629.1974610-2-chengzhihao1@huawei.com>
Date: Mon, 15 May 2023 21:36:28 +0800
From: Zhihao Cheng <chengzhihao1@...wei.com>
To: <miklos@...redi.hu>, <amir73il@...il.com>, <brauner@...nel.org>
CC: <linux-unionfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<chengzhihao1@...wei.com>
Subject: [PATCH v2 1/2] ovl: ovl_permission: Fix null pointer dereference at realinode in rcu-walk mode
Following process:
P1 P2
path_lookupat
link_path_walk
inode_permission
ovl_permission
ovl_i_path_real(inode, &realpath)
path->dentry = ovl_i_dentry_upper(inode)
drop_cache
__dentry_kill(ovl_dentry)
iput(ovl_inode)
ovl_destroy_inode(ovl_inode)
dput(oi->__upperdentry)
dentry_kill(upperdentry)
dentry_unlink_inode
upperdentry->d_inode = NULL
realinode = d_inode(realpath.dentry) // return NULL
inode_permission(realinode)
inode->i_sb // NULL pointer dereference
, will trigger an null pointer dereference at realinode:
[ 335.664979] BUG: kernel NULL pointer dereference,
address: 0000000000000002
[ 335.668032] CPU: 0 PID: 2592 Comm: ls Not tainted 6.3.0
[ 335.669956] RIP: 0010:inode_permission+0x33/0x2c0
[ 335.678939] Call Trace:
[ 335.679165] <TASK>
[ 335.679371] ovl_permission+0xde/0x320
[ 335.679723] inode_permission+0x15e/0x2c0
[ 335.680090] link_path_walk+0x115/0x550
[ 335.680771] path_lookupat.isra.0+0xb2/0x200
[ 335.681170] filename_lookup+0xda/0x240
[ 335.681922] vfs_statx+0xa6/0x1f0
[ 335.682233] vfs_fstatat+0x7b/0xb0
Fetch a reproducer in [Link].
Add a new helper ovl_i_path_realinode() to get realpath and real inode
after non-nullptr checking, use the helper to replace the current realpath
getting logic.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217405
Fixes: 4b7791b2e958 ("ovl: handle idmappings in ovl_permission()")
Signed-off-by: Zhihao Cheng <chengzhihao1@...wei.com>
Suggested-by: Christian Brauner <brauner@...nel.org>
---
fs/overlayfs/inode.c | 31 ++++++++++++++++++++++++-------
1 file changed, 24 insertions(+), 7 deletions(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 541cf3717fc2..cc3ef5a6666a 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -278,6 +278,26 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path,
return err;
}
+static inline int ovl_i_path_realinode(struct inode *inode,
+ struct path *realpath,
+ struct inode **realinode, int rcu)
+{
+ /* Careful in RCU walk mode */
+ ovl_i_path_real(inode, realpath);
+ if (!realpath->dentry) {
+ WARN_ON(!rcu);
+ return -ECHILD;
+ }
+
+ *realinode = d_inode(realpath->dentry);
+ if (!*realinode) {
+ WARN_ON(!rcu);
+ return -ECHILD;
+ }
+
+ return 0;
+}
+
int ovl_permission(struct mnt_idmap *idmap,
struct inode *inode, int mask)
{
@@ -287,12 +307,10 @@ int ovl_permission(struct mnt_idmap *idmap,
const struct cred *old_cred;
int err;
- /* Careful in RCU walk mode */
- ovl_i_path_real(inode, &realpath);
- if (!realpath.dentry) {
- WARN_ON(!(mask & MAY_NOT_BLOCK));
- return -ECHILD;
- }
+ err = ovl_i_path_realinode(inode, &realpath, &realinode,
+ mask & MAY_NOT_BLOCK);
+ if (err)
+ return err;
/*
* Check overlay inode with the creds of task and underlying inode
@@ -302,7 +320,6 @@ int ovl_permission(struct mnt_idmap *idmap,
if (err)
return err;
- realinode = d_inode(realpath.dentry);
old_cred = ovl_override_creds(inode->i_sb);
if (!upperinode &&
!special_file(realinode->i_mode) && mask & MAY_WRITE) {
--
2.39.2
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