linux-kernel - Re: [PATCH] nilfs2: fix CFI failure when accessing /sys/fs/nilfs2/features/*

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Message-ID: <CAKFNMo=yfPPn0bc+vGv4f3yhyOQy33+ZHJJGURyY9NaHaRtToQ@mail.gmail.com>
Date: Sat, 6 Sep 2025 12:49:43 +0900
From: Ryusuke Konishi <konishi.ryusuke@...il.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Kees Cook <kees@...nel.org>, linux-nilfs@...r.kernel.org, 
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org, kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH] nilfs2: fix CFI failure when accessing /sys/fs/nilfs2/features/*

On Sat, Sep 6, 2025 at 4:24 AM Nathan Chancellor wrote:
>
> When accessing one of the files under /sys/fs/nilfs2/features when
> CONFIG_CFI_CLANG is enabled, there is a CFI violation:
>
>   CFI failure at kobj_attr_show+0x59/0x80 (target: nilfs_feature_revision_show+0x0/0x30; expected type: 0xfc392c4d)
>   ...
>   Call Trace:
>    <TASK>
>    sysfs_kf_seq_show+0x2a6/0x390
>    ? __cfi_kobj_attr_show+0x10/0x10
>    kernfs_seq_show+0x104/0x15b
>    seq_read_iter+0x580/0xe2b
>   ...
>
> When the kobject of the kset for /sys/fs/nilfs2 is initialized, its
> ktype is set to kset_ktype, which has a ->sysfs_ops of kobj_sysfs_ops.
> When nilfs_feature_attr_group is added to that kobject via
> sysfs_create_group(), the kernfs_ops of each files is
> sysfs_file_kfops_rw, which will call sysfs_kf_seq_show() when
> ->seq_show() is called. sysfs_kf_seq_show() in turn calls
> kobj_attr_show() through ->sysfs_ops->show(). kobj_attr_show() casts the
> provided attribute out to a 'struct kobj_attribute' via container_of()
> and calls ->show(), resulting in the CFI violation since neither
> nilfs_feature_revision_show() nor nilfs_feature_README_show() match the
> prototype of ->show() in 'struct kobj_attribute'.
>
> Resolve the CFI violation by adjusting the second parameter in
> nilfs_feature_{revision,README}_show() from 'struct attribute' to
> 'struct kobj_attribute' to match the expected prototype.
>
> Cc: stable@...r.kernel.org
> Fixes: aebe17f68444 ("nilfs2: add /sys/fs/nilfs2/features group")
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202509021646.bc78d9ef-lkp@intel.com/
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Thanks again!
I'll send this upstream.

Regards,
Ryusuke Konishi