From: Zhihao Cheng chengzhihao1@huawei.com
commit 1a73f5b8f079fd42a544c1600beface50c63af7c upstream.
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].
Use the helper ovl_i_path_realinode() to get realinode and then do non-nullptr checking.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217405 Fixes: 4b7791b2e958 ("ovl: handle idmappings in ovl_permission()") Cc: stable@vger.kernel.org # v5.19 Signed-off-by: Zhihao Cheng chengzhihao1@huawei.com Suggested-by: Christian Brauner brauner@kernel.org Suggested-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/overlayfs/inode.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
--- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -286,8 +286,8 @@ int ovl_permission(struct user_namespace int err;
/* Careful in RCU walk mode */ - ovl_i_path_real(inode, &realpath); - if (!realpath.dentry) { + realinode = ovl_i_path_real(inode, &realpath); + if (!realinode) { WARN_ON(!(mask & MAY_NOT_BLOCK)); return -ECHILD; } @@ -300,7 +300,6 @@ int ovl_permission(struct user_namespace 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) {