The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x f4e19e595cc2e76a8a58413eb19d3d9c51328b53 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2023071621-charcoal-prewashed-932b@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: f4e19e595cc2 ("ovl: fix null pointer dereference in ovl_get_acl_rcu()") 6c0a8bfb84af ("ovl: implement get acl method") cac2f8b8d8b5 ("fs: rename current get acl method") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From f4e19e595cc2e76a8a58413eb19d3d9c51328b53 Mon Sep 17 00:00:00 2001 From: Zhihao Cheng <chengzhihao1@xxxxxxxxxx> Date: Tue, 16 May 2023 22:16:19 +0800 Subject: [PATCH] ovl: fix null pointer dereference in ovl_get_acl_rcu() 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]. 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=217404 Fixes: 332f606b32b6 ("ovl: enable RCU'd ->get_acl()") Cc: <stable@xxxxxxxxxxxxxxx> # v5.15 Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx> Suggested-by: Christian Brauner <brauner@xxxxxxxxxx> Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index ca56b1328a2c..e7e888dea634 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -558,20 +558,20 @@ 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; - if (!IS_POSIXACL(realinode)) - return NULL; - /* 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(!rcu); return ERR_PTR(-ECHILD); } + if (!IS_POSIXACL(realinode)) + return NULL; + if (rcu) { /* * If the layer is idmapped drop out of RCU path walk
