From ae146bc1abdeb4607abf2975b858c053024e8ac1 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Mon, 21 Sep 2026 12:40:13 +0200 Subject: [PATCH] ovl: fix UAF in ovl_do_mkdir() debug print ovl_do_mkdir() prints the input dentry with %pd after vfs_mkdir(). Since commit fe497f0759e0 ("VFS: change vfs_mkdir() to unlock on failure."), vfs_mkdir() calls end_creating() on the input dentry on failure and may replace it on success, so the post-call %pd can use-after-free the dentry when CONFIG_OVERLAY_FS_DEBUG is enabled. Print the dentry before the call and only the result afterward. Reported-by: syzbot+ced26b784bf977d223dd@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=ced26b784bf977d223dd Fixes: fe497f0759e0 ("VFS: change vfs_mkdir() to unlock on failure.") Signed-off-by: Amir Goldstein Link: https://patch.msgid.link/20260921104013.40475-1-amir73il@gmail.com Signed-off-by: Christian Brauner (Amutable) --- fs/overlayfs/overlayfs.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h index e0d8c6152e9f..7f3558372c59 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -254,8 +254,10 @@ static inline struct dentry *ovl_do_mkdir(struct ovl_fs *ofs, { struct dentry *ret; + /* vfs_mkdir() drops @dentry on failure and may replace it on success */ + pr_debug("mkdir(%pd2, 0%o)\n", dentry, mode); ret = vfs_mkdir(ovl_upper_mnt_idmap(ofs), dir, dentry, mode, NULL); - pr_debug("mkdir(%pd2, 0%o) = %i\n", dentry, mode, PTR_ERR_OR_ZERO(ret)); + pr_debug("...mkdir = %i\n", PTR_ERR_OR_ZERO(ret)); return ret; }