[LTP] [PATCH v1] overcommit_memory: Fix integer overflow and 32-bit limits

[Ben Copeland]

The overcommit test uses sum_total, the sum (memory and swap) to test
the overcommit settings.

This fixes two problems on 32-bit systems. The first is seen with a
integer overflow can occur when calculating sum_total * 2, if the
sum_total is larger than 2GB. The second is limited virtual address
space (2-3GB) means the test can fail from address space exhaustion
before overcommit has been tested.

Now the test runs correctly on low-memory 32-bit systems while avoiding
both the overflow bug and virtual address space issues.

Signed-off-by: Ben Copeland <ben.copeland@linaro.org>
---
 .../kernel/mem/tunable/overcommit_memory.c    | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/testcases/kernel/mem/tunable/overcommit_memory.c b/testcases/kernel/mem/tunable/overcommit_memory.c
index 9b2cb479d..f9f60ebc3 100644
--- a/testcases/kernel/mem/tunable/overcommit_memory.c
+++ b/testcases/kernel/mem/tunable/overcommit_memory.c
@@ -68,6 +68,7 @@
 #define DEFAULT_OVER_RATIO	50L
 #define EXPECT_PASS		0
 #define EXPECT_FAIL		1
+#define ONE_GB			(1024 * 1024 * TST_KB)
 
 #define OVERCOMMIT_MEMORY "/proc/sys/vm/overcommit_memory"
 #define OVERCOMMIT_RATIO "/proc/sys/vm/overcommit_ratio"
@@ -141,14 +142,26 @@ static void overcommit_memory_test(void)
 
 	update_mem();
 	alloc_and_check(free_total / 2, EXPECT_PASS);
-	alloc_and_check(sum_total * 2, EXPECT_FAIL);
+	/* Skip if sum_total * 2 would exceed address space.
+	 * On 32-bit, skip when sum_total > ULONG_MAX/4 (~1GB).
+	 * Most 32-bit systems with <=1GB RAM can map 2x that in 3GB vaddr space.
+	 * Systems with 2GB+ RAM likely cannot fit allocations in vaddr space. */
+	if (tst_kernel_bits() == 64 || (unsigned long)sum_total <= ONE_GB) {
+		alloc_and_check(sum_total * 2, EXPECT_FAIL);
+	} else {
+		tst_res(TCONF, "Skipping large allocation test due to address space limits");
+	}
 
 	/* start to test overcommit_memory=1 */
 	TST_SYS_CONF_LONG_SET(OVERCOMMIT_MEMORY, 1, 1);
 
 	alloc_and_check(sum_total / 2, EXPECT_PASS);
-	alloc_and_check(sum_total, EXPECT_PASS);
-	alloc_and_check(sum_total * 2, EXPECT_PASS);
+	if (tst_kernel_bits() == 64 || (unsigned long)sum_total <= ONE_GB) {
+		alloc_and_check(sum_total, EXPECT_PASS);
+		alloc_and_check(sum_total * 2, EXPECT_PASS);
+	} else {
+		tst_res(TCONF, "Skipping large allocation tests due to address space limits");
+	}
 
 }
 
-- 
2.51.0