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

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

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.

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