Re: [Qemu-devel] Fix for accept

[Fabrice Bellard <fabrice@bellard.org>]

Hi,

OK for the bug report, but the fix is not correct because the problem is 
generic. [get|put]_user() and the other functions should be used 
everywhere to communicate with the "user" space and to generate the 
-EFAULT error if the address is not correct. For that purpose the host 
signal SIGSEGV can be catched and asm macros can be used to see if it is 
an expected seg fault (in this case [get|put]_user must return an error 
code) or if it is a QEMU bug. Note that exactly the same system is used 
inside the Linux kernel and I don't think it is necessary to invent 
something else.

Regards,

Fabrice.

Pablo Virolainen wrote:
> Following code crashes qemu user emulation.
> 
> #include <sys/types.h>
> #include <sys/socket.h>
> 
> int main() {
>         accept(0,NULL,NULL);
>         return 0;
> }
> 
> Pablo Virolainen
> 
> 
> ------------------------------------------------------------------------
> 
> Index: linux-user/syscall.c
> ===================================================================
> RCS file: /sources/qemu/qemu/linux-user/syscall.c,v
> retrieving revision 1.75
> diff -u -r1.75 syscall.c
> --- linux-user/syscall.c	27 Jun 2006 21:08:10 -0000	1.75
> +++ linux-user/syscall.c	13 Jul 2006 10:18:57 -0000
> @@ -878,9 +878,20 @@
>              int sockfd = tgetl(vptr);
>              target_ulong target_addr = tgetl(vptr + n);
>              target_ulong target_addrlen = tgetl(vptr + 2 * n);
> -            socklen_t addrlen = tget32(target_addrlen);
> -            void *addr = alloca(addrlen);
> -
> +            socklen_t addrlen=0;
> +	    /* Just to get rid of compiler warnings */
> +	    ulong addrt=0;
> +            void *addr;
> +	    
> +	    get_user(addrlen,&target_addrlen);
> +	    get_user(addrt,&target_addr);
> +	    
> +	    if (addrt!=0) {
> +	        addr = alloca(addrlen);
> +	    } else {
> +	        addr = NULL;
> +	    }
> +	    
>              ret = get_errno(accept(sockfd, addr, &addrlen));
>              if (!is_error(ret)) {
>                  host_to_target_sockaddr(target_addr, addr, addrlen);
> 
> 
> ------------------------------------------------------------------------
> 
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