Subject: Re: [PATCH v2 3/5] signal: Add unsafe_copy_siginfo_to_user()

From: [email-masked] (Eric W. Biederman)
Date: Thu, 02 Sep 2021 13:43:05 -0500

Christophe Leroy <[email-masked]> writes:

> In the same spirit as commit fb05121fd6a2 ("signal: Add
> unsafe_get_compat_sigset()"), implement an 'unsafe' version of
> copy_siginfo_to_user() in order to use it within user access blocks.
>
> For that, also add an 'unsafe' version of clear_user().

Looking at your use cases you need the 32bit compat version of this
as well.

The 32bit compat version is too complicated to become a macro, so I
don't think you can make this work correctly for the 32bit compat case.

Probably-Not-by: "Eric W. Biederman" <[email-masked]>

Eric

> Signed-off-by: Christophe Leroy <[email-masked]>
> ---
>  include/linux/signal.h  | 15 +++++++++++++++
>  include/linux/uaccess.h |  1 +
>  kernel/signal.c         |  5 -----
>  3 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/signal.h b/include/linux/signal.h
> index 3454c7ff0778..659bd43daf10 100644
> --- a/include/linux/signal.h
> +++ b/include/linux/signal.h
> @@ -35,6 +35,21 @@ static inline void copy_siginfo_to_external(siginfo_t *to,
>  int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from);
>  int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from);
>  
> +static __always_inline char __user *si_expansion(const siginfo_t __user *info)
> +{
> +	return ((char __user *)info) + sizeof(struct kernel_siginfo);
> +}
> +
> +#define unsafe_copy_siginfo_to_user(to, from, label) do {		\
> +	siginfo_t __user *__ucs_to = to;				\
> +	const kernel_siginfo_t *__ucs_from = from;			\
> +	char __user *__ucs_expansion = si_expansion(__ucs_to);		\
> +									\
> +	unsafe_copy_to_user(__ucs_to, __ucs_from,			\
> +			    sizeof(struct kernel_siginfo), label);	\
> +	unsafe_clear_user(__ucs_expansion, SI_EXPANSION_SIZE, label);	\
> +} while (0)
> +
>  enum siginfo_layout {
>  	SIL_KILL,
>  	SIL_TIMER,
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index c05e903cef02..37073caac474 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -398,6 +398,7 @@ long strnlen_user_nofault(const void __user *unsafe_addr, long count);
>  #define unsafe_put_user(x,p,e) unsafe_op_wrap(__put_user(x,p),e)
>  #define unsafe_copy_to_user(d,s,l,e) unsafe_op_wrap(__copy_to_user(d,s,l),e)
>  #define unsafe_copy_from_user(d,s,l,e) unsafe_op_wrap(__copy_from_user(d,s,l),e)
> +#define unsafe_clear_user(d, l, e) unsafe_op_wrap(__clear_user(d, l), e)
>  static inline unsigned long user_access_save(void) { return 0UL; }
>  static inline void user_access_restore(unsigned long flags) { }
>  #endif
> diff --git a/kernel/signal.c b/kernel/signal.c
> index a3229add4455..83b5971e4304 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -3261,11 +3261,6 @@ enum siginfo_layout siginfo_layout(unsigned sig, int si_code)
>  	return layout;
>  }
>  
> -static inline char __user *si_expansion(const siginfo_t __user *info)
> -{
> -	return ((char __user *)info) + sizeof(struct kernel_siginfo);
> -}
> -
>  int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from)
>  {
>  	char __user *expansion = si_expansion(to);