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

[Christophe Leroy]

Le 02/09/2021 à 20:43, Eric W. Biederman a écrit :
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> 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@xxxxxxxxxxxx>
>
> Eric
>
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> > ---
> >   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);