From: Breno Leitao <leitao@debian.org>
To: Vasileios Almpanis <vasilisalmpanis@gmail.com>
Cc: Andreas Hindborg <a.hindborg@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org,
syzbot+6b16e3d085833cbf3e25@syzkaller.appspotmail.com
Subject: Re: [PATCH 2/2] configfs: unhash the dentry before dropping the item in rmdir
Date: Fri, 31 Jul 2026 02:29:58 -0700 [thread overview]
Message-ID: <amxrCqfgaWnoWcte@gmail.com> (raw)
In-Reply-To: <20260730093435.195441-3-vasilisalmpanis@gmail.com>
On Thu, Jul 30, 2026 at 11:30:25AM +0200, Vasileios Almpanis wrote:
> configfs_get_config_item() treats a hashed dentry as proof that
> sd->s_element is a live config_item. configfs_rmdir() breaks that:
> simple_rmdir() leaves the dentry hashed, the last reference to the item is
> dropped right after, and the dentry is only unhashed by d_delete() once
> ->rmdir() has returned. configfs_symlink() resolves its target holding no
> lock on it, so get_target() can land in that window:
>
> BUG: KASAN: slab-use-after-free in config_item_get+0x26/0x90
> get_target fs/configfs/symlink.c:128 [inline]
> configfs_symlink+0x4ab/0x1030 fs/configfs/symlink.c:185
>
> Unhash in configfs_remove_dir(), while the item is still guaranteed to be
> there. A reference obtained just before that stays harmless, as
> create_link() rechecks CONFIGFS_USET_DROPPING, already set by
> configfs_detach_prep(). Both configfs_unregister_subsystem() paths
> d_drop() after detaching, so this only makes rmdir match them.
Is the claim that "a reference obtained just before that stays harmless,
as create_link() rechecks CONFIGFS_USET_DROPPING" accurate?
next prev parent reply other threads:[~2026-07-31 9:30 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-30 9:30 [PATCH 0/2] configfs: fix use-after-free of symlink target racing with rmdir Vasileios Almpanis
2026-07-30 9:30 ` [PATCH 1/2] configfs: pin the symlink target's dirent instead of chasing ->ci_dentry Vasileios Almpanis
2026-07-30 9:30 ` [PATCH 2/2] configfs: unhash the dentry before dropping the item in rmdir Vasileios Almpanis
2026-07-31 9:29 ` Breno Leitao [this message]
2026-07-31 9:55 ` Vasileios Almpanis
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