user/mbuffer: add patch to clamp 32-bit parameters. fixes #834.

The number of physical and available pages will of course be
correct on real 32-bit systems, but mbuffer does not account
for the case of when a 64-bit system with more memory is
running with a 32-bit personality. In this scenario, dynamic
detection of system memory limits yields values that are not
safe for use in a 32-bit environment.

1 files changed, 39 insertions, 0 deletions

diff --git a/user/mbuffer/clamp-32-bit-parameters.patch b/user/mbuffer/clamp-32-bit-parameters.patch
new file mode 100644
index 000000000..3dc2d0eac
--- /dev/null
+++ b/user/mbuffer/clamp-32-bit-parameters.patch
@@ -0,0 +1,39 @@
+In addition to clamping NumP and AvP, this patch reorders
+shift operations to prevent possible overflow when given
+values that are found in some environments where a 64-bit
+system is running with a 32-bit personality.
+
+It should not be construed as fixing any bug in mbuffer.
+
+--- a/mbuffer.c
++++ b/mbuffer.c
+@@ -984,7 +984,14 @@
+ 
+ 	/* get physical memory size */
+ #if defined(_SC_PHYS_PAGES)
+-	NumP = sysconf(_SC_PHYS_PAGES);
++	if (sizeof(void *) == 4)
++	{
++		NumP = (unsigned)-1 / PgSz; /* 4GB worth of pages */
++	}
++	else
++	{
++		NumP = sysconf(_SC_PHYS_PAGES);
++	}
+ 	if (NumP < 0) {
+ 		warningmsg("unable to determine number of total memory pages: %s\n",strerror(errno));
+ 		NumP = 0;
+@@ -1004,8 +1011,12 @@
+ 			char *at = strstr(tmp,"MemAvailable:");
+ 			if (at) {
+ 				AvP = strtol(at+13,0,0);
+-				AvP <<= 10;
+ 				AvP /= PgSz;
++				AvP <<= 10;
++				if (sizeof(void *) == 4 && AvP > NumP)
++				{
++					AvP = NumP;
++				}
+ 				debugmsg("available memory: %lu pages\n",AvP);
+ 			}
+ 		}