在 2023/5/16 19:40, Amir Goldstein 写道:
On Mon, May 15, 2023 at 4:39 PM Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote:Following process: P1 P2 path_openat link_path_walk may_lookup inode_permission(rcu) ovl_permission acl_permission_check check_acl get_cached_acl_rcu ovl_get_inode_acl realinode = ovl_inode_real(ovl_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 ovl_inode_upper upperdentry = ovl_i_dentry_upper(ovl_inode) d_inode(upperdentry) // returns NULL IS_POSIXACL(realinode) // NULL pointer dereference , will trigger an null pointer dereference at realinode: [ 205.472797] BUG: kernel NULL pointer dereference, address: 0000000000000028 [ 205.476701] CPU: 2 PID: 2713 Comm: ls Not tainted 6.3.0-12064-g2edfa098e750-dirty #1216 [ 205.478754] RIP: 0010:do_ovl_get_acl+0x5d/0x300 [ 205.489584] Call Trace: [ 205.489812] <TASK> [ 205.490014] ovl_get_inode_acl+0x26/0x30 [ 205.490466] get_cached_acl_rcu+0x61/0xa0 [ 205.490908] generic_permission+0x1bf/0x4e0 [ 205.491447] ovl_permission+0x79/0x1b0 [ 205.491917] inode_permission+0x15e/0x2c0 [ 205.492425] link_path_walk+0x115/0x550 [ 205.493311] path_lookupat.isra.0+0xb2/0x200 [ 205.493803] filename_lookup+0xda/0x240 [ 205.495747] vfs_fstatat+0x7b/0xb0 Fetch a reproducer in [Link]. Fix it by using helper ovl_i_path_realinode() to get realpath and real inode after non-nullptr checking. Link: https://bugzilla.kernel.org/show_bug.cgi?id=217404 Fixes: 332f606b32b6 ("ovl: enable RCU'd ->get_acl()")Note that this bug is also in 5.15.y, in method ovl_get_acl(). I hope you will be able to follow up with a simple backport for 5.15 - i.e. only need to add a check for NULL realinode at the beginning. There was no realpath back then.
Sure. I notice that there is a '[ Upstream commit xxx ]' field in 5.15 patch, so may I backport it after the fix applied into mainline(6.4)?
AFAICT, both your patches should apply cleanly to 6.1.y, so should be picked up automatically by stable kernel bots. Thanks, Amir.Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx> Suggested-by: Christian Brauner <brauner@xxxxxxxxxx> --- fs/overlayfs/inode.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index cc3ef5a6666a..b2021eada8be 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -576,20 +576,18 @@ struct posix_acl *do_ovl_get_acl(struct mnt_idmap *idmap, struct inode *inode, int type, bool rcu, bool noperm) { - struct inode *realinode = ovl_inode_real(inode); + struct inode *realinode; struct posix_acl *acl; struct path realpath; + int err; + + err = ovl_i_path_realinode(inode, &realpath, &realinode, rcu); + if (err) + return ERR_PTR(err); if (!IS_POSIXACL(realinode)) return NULL; - /* Careful in RCU walk mode */ - ovl_i_path_real(inode, &realpath); - if (!realpath.dentry) { - WARN_ON(!rcu); - return ERR_PTR(-ECHILD); - } - if (rcu) { /* * If the layer is idmapped drop out of RCU path walk -- 2.39.2.
