[PATCH] fix decoding of sysctl() when oldval fields are NULL

[Mike Frysinger]

If you call glibc's syscall wrapper like so:
	static int name[] = { CTL_NET, NET_IPV4, NET_IPV4_LOCAL_PORT_RANGE };
	int buffer[2] = { 32768, 61000 };
	size_t size = sizeof(buffer);
	sysctl(name, 3, 0, 0, buffer, size);
(note that oldval/oldlenp are NULL).

The current strace code complains like so:
_sysctl({{CTL_NET, NET_IPV4, NET_IPV4_LOCAL_PORT_RANGE, 38}, 3, process_vm_readv: Bad address
(nil), 0, 0x7fffe23c3960, 8}) = -1 EACCES (Permission denied)

Since passing NULL for the old values is valid, handle that explicitly.
This also simplifies the code a bit by splitting up the handling of the
new and old args so that we only handle the new args once.

Now the output looks like:
_sysctl({{CTL_NET, NET_IPV4, NET_IPV4_LOCAL_PORT_RANGE, 38}, 3, NULL, 0, 0x7fff8c0c91b0, 8) = -1 EACCES (Permission denied)

* system.c (sys_sysctl): Check if info.oldval is NULL first.  Move the
processing of oldlen/info.newval/info.newlen out so they always get
executed.  Fix the format strings so we use %lu for unsigned long rather
than a mix of %ld and %lu.

Signed-off-by: Mike Frysinger <vapier at gentoo.org>
---
 system.c | 38 +++++++++++++++++++-------------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/system.c b/system.c
index ef34b95..04f7279 100644
--- a/system.c
+++ b/system.c
@@ -954,32 +954,32 @@ sys_sysctl(struct tcb *tcp)
 		tprintf("}, %d, ", info.nlen);
 	} else {
 		size_t oldlen = 0;
-		if (umove(tcp, (long)info.oldlenp, &oldlen) >= 0
-		    && info.nlen >= 2
-		    && ((name[0] == CTL_KERN
-			 && (name[1] == KERN_OSRELEASE
-			     || name[1] == KERN_OSTYPE
+		if (info.oldval == NULL) {
+			tprints("NULL");
+		} else if (umove(tcp, (long)info.oldlenp, &oldlen) >= 0
+			   && info.nlen >= 2
+			   && ((name[0] == CTL_KERN
+				&& (name[1] == KERN_OSRELEASE
+				    || name[1] == KERN_OSTYPE
 #ifdef KERN_JAVA_INTERPRETER
-			     || name[1] == KERN_JAVA_INTERPRETER
+				    || name[1] == KERN_JAVA_INTERPRETER
 #endif
 #ifdef KERN_JAVA_APPLETVIEWER
-			     || name[1] == KERN_JAVA_APPLETVIEWER
+				    || name[1] == KERN_JAVA_APPLETVIEWER
 #endif
-				 )))) {
+					)))) {
 			printpath(tcp, (size_t)info.oldval);
-			tprintf(", %lu, ", (unsigned long)oldlen);
-			if (info.newval == 0)
-				tprints("NULL");
-			else if (syserror(tcp))
-				tprintf("%p", info.newval);
-			else
-				printpath(tcp, (size_t)info.newval);
-			tprintf(", %ld}", (unsigned long)info.newlen);
 		} else {
-			tprintf("%p, %ld, %p, %ld}",
-				info.oldval, (unsigned long)oldlen,
-				info.newval, (unsigned long)info.newlen);
+			tprintf("%p", info.oldval);
 		}
+		tprintf(", %lu, ", (unsigned long)oldlen);
+		if (info.newval == NULL)
+			tprints("NULL");
+		else if (syserror(tcp))
+			tprintf("%p", info.newval);
+		else
+			printpath(tcp, (size_t)info.newval);
+		tprintf(", %lu", (unsigned long)info.newlen);
 	}
 
 	free(name);
-- 
1.8.0.2