Re: [Qemu-devel] Fix for accept
Fabrice Bellard wrote:
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.
Hello,
So I should write something like following instead?
if (!get_user(addrlen,target_addrlen)) {
return -EFAULT
}
The code seems to assume target_sockaddr == sockaddr, so why allocate
temporary buffer and then do copying?
One could implement SOCKOP_[accept|getsockname|getpeername] with same
code. Perhaps something like
static long do_socketcall_helper(target_ulong vptr,
int (*func)(int,struct sockaddr*,socklen_t*))
{
const int n = sizeof(target_ulong);
if (access_ok(VERIFY_READ,vptr,n*3)) {
int ret;
int sockfd=tgetl(vptr);
target_ulong target_addr = tgetl(vptr + n);
target_ulong target_addrlen = tgetl(vptr + 2 * n);
struct sockaddr *addr=(struct sockaddr *)target_addr;
socklen_t addrlen;
if (!get_user(addrlen,target_addrlen) ||
!acces_ok(VERIFY_WRITE,target_addrlen,4)) {
return -EFAULT;
}
ret=get_errno(func(sockfd, addr, addrlen));
if (!is_error(ret)) {
host_to_target_sockaddr(target_addr, addr, addrlen);
tput32(target_addrlen, addrlen);
}
return ret;
}
return -EFAULT;
}
case SOCKOP_accept:
ret = do_socketcall_helper(vptr,accept);
break;
case SOCKOP_getsockname:
ret = do_socketcall_helper(vptr,getsockname);
break;
case SOCKOP_getpeername:
ret = do_socketcall_helper(vptr,getpeername);
break;
Pablo
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Re: [Qemu-devel] Fix for accept
Pablo Virolainen wrote:
So I should write something like following instead?
if (!get_user(addrlen,target_addrlen)) {
return -EFAULT
}
Yes.
The code seems to assume target_sockaddr == sockaddr, so why allocate
temporary buffer and then do copying?
If the assumption target_sockaddr == sockaddr is made, then it is a bug.
One could implement SOCKOP_[accept|getsockname|getpeername] with same
code.
[...]
You can use common code, but I think it is clearer to have the
do_accept, do_getsockname and do_getpeername helpers.
Fabrice.
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Re: [Qemu-devel] Fix for accept
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.c27 Jun 2006 21:08:10 - 1.75
+++ linux-user/syscall.c13 Jul 2006 10:18:57 -
@@ -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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