Re: [PATCH v2] malloc: Do not clobber errno on __getrandom_nocancel (BZ#29624)

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Sep 29, 2022 at 12:09 PM Adhemerval Zanella Netto via
Libc-alpha <libc-alpha@sourceware.org> wrote:
>
>
>
> On 29/09/22 15:36, Wilco Dijkstra wrote:
> > Hi Adhemerval,
> >
> > Another question, the syscall is defined as:
> >
> > ssize_t getrandom (void *__buffer, size_t __length,
> >
> > Doesn't this mean if we use 'int' for the return value, a large but valid syscall
> > result could be interpreted as a negative error value? It sounds like all code
> > processing the getrandom syscall should use ssize_t rather than int. Or do we
> > limit length to something fairly small?
>
> Yeah, you are right.  The syscall indeed returns ssize_t/long:
>
> include/linux/syscalls.h:1007:asmlinkage long sys_getrandom(char __user *buf, size_t count,
>
> So it does make sense to use ssize_t. It seems that not all architectures handle
> INTERNAL_SYSCALL consistently to use 'long', but at least the 64 bits does.

I think it should be __syscall_slong_t since sys_getrandom will return 64-bit
integer for x32.

> It also handles the issue raised by Yann, where arc4random fallback is not used.
> This is in fact another issue and I will send an independently patch.
>
> >
> >  __arc4random_buf (void *p, size_t n)
> >  {
> >    static int seen_initialized;
> > -  size_t l;
> > +  int l;
> >
> > Should be ssize_t?
> >
> > +static inline int
> > +__getrandom_nocancel (void *buf, size_t buflen, unsigned int flags)
> >
> > ssize_t?
> >
> > +{
> > +  int save_errno = errno;
> > +  int r = __getrandom (buf, buflen, flags);
> >
> > ssize_t?
> >
> > +  r = r == -1 ? -errno : r;
> > +  __set_errno (save_errno);
> > +  return r;
> > +}
> >
> >  #define __poll_infinity_nocancel(fds, nfds) \
> >    __poll (fds, nfds, -1)
> > diff --git a/sysdeps/unix/sysv/linux/not-cancel.h b/sysdeps/unix/sysv/linux/not-cancel.h
> > index a263d294b1..00ab75a405 100644
> > --- a/sysdeps/unix/sysv/linux/not-cancel.h
> > +++ b/sysdeps/unix/sysv/linux/not-cancel.h
> > @@ -71,7 +71,7 @@ __writev_nocancel_nostatus (int fd, const struct iovec *iov, int iovcnt)
> >  static inline int
> >
> > ssize_t?
> >
> >  __getrandom_nocancel (void *buf, size_t buflen, unsigned int flags)
> >  {
> > -  return INLINE_SYSCALL_CALL (getrandom, buf, buflen, flags);
> > +  return INTERNAL_SYSCALL_CALL (getrandom, buf, buflen, flags);
> >  }
> >
> > Cheers,
> > Wilco



-- 
H.J.