On Tue, Jan 03, 2023 at 03:46:20PM -0800, Kees Cook wrote:
> With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
> indirect call targets are validated against the expected function
> pointer prototype to make sure the call target is valid to help mitigate
> ROP attacks. If they are not identical, there is a failure at run time,
> which manifests as either a kernel panic or thread getting killed.
>
> ext4_feat_ktype was setting the "release" handler to "kfree", which
> doesn't have a matching function prototype. Add a simple wrapper
> with the correct prototype.
>
> This was found as a result of Clang's new -Wcast-function-type-strict
> flag, which is more sensitive than the simpler -Wcast-function-type,
> which only checks for type width mismatches.
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
> fs/ext4/sysfs.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index d233c24ea342..83cf8b5afb54 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -491,6 +491,11 @@ static void ext4_sb_release(struct kobject *kobj)
> complete(&sbi->s_kobj_unregister);
> }
>
> +static void ext4_kobject_release(struct kobject *kobj)
> +{
> + kfree(kobj);
> +}
> +
> static const struct sysfs_ops ext4_attr_ops = {
> .show = ext4_attr_show,
> .store = ext4_attr_store,
> @@ -505,7 +510,7 @@ static struct kobj_type ext4_sb_ktype = {
> static struct kobj_type ext4_feat_ktype = {
> .default_groups = ext4_feat_groups,
> .sysfs_ops = &ext4_attr_ops,
> - .release = (void (*)(struct kobject *))kfree,
> + .release = ext4_kobject_release,
> };
>
> void ext4_notify_error_sysfs(struct ext4_sb_info *sbi)
> --
> 2.34.1
>
