linux-kernel - Re: [PATCH v2 3/5] signal: Add unsafe_copy_siginfo_to

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Message-ID: <2715792c-eb10-eeb8-3d49-24486abe953b@csgroup.eu>
Date:   Fri, 3 Sep 2021 10:56:14 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 3/5] signal: Add unsafe_copy_siginfo_to_user()



Le 02/09/2021 à 20:43, Eric W. Biederman a écrit :
> Christophe Leroy <christophe.leroy@...roup.eu> 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.

When looking into patch 5/5 that you nacked, I think you missed the fact that we keep using 
copy_siginfo_to_user32() as it for the 32 bit compat case.

> 
> Probably-Not-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> 
> Eric
> 
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   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);