On Tue, May 16, 2023 at 5:19 PM Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote: > > 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()") > Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx> > Suggested-by: Christian Brauner <brauner@xxxxxxxxxx> > Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx> Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx> > --- > fs/overlayfs/inode.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c > index 541cf3717fc2..ca56b1328a2c 100644 > --- a/fs/overlayfs/inode.c > +++ b/fs/overlayfs/inode.c > @@ -288,8 +288,8 @@ int ovl_permission(struct mnt_idmap *idmap, > 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; > } > @@ -302,7 +302,6 @@ 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 >
