Consider cgroup when determining memory usage

This change modifies the oscap_sys_memusage function
to take into account the memory constraints of the
cgroup. Both cgroup and cgroup2 are supported.

Author: 0intro

src/common/memusage.c

@@ -48,9 +48,9 @@
 #define GET_VM_FREE_PAGE_COUNT  "vm.stats.vm.v_free_count"
 #define GET_VM_INACT_PAGE_COUNT "vm.stats.vm.v_inactive_count"
 #define GET_VM_ACT_PAGE_COUNT   "vm.stats.vm.v_active_count"
+#endif
 
 #define BYTES_TO_KIB(x) (x >> 10)
-#endif
 
 #include "debug_priv.h"
 #include "memusage.h"
@@ -173,6 +173,26 @@ static int read_status(const char *source, void *base, struct stat_parser *spt,
 	return processed == spt_size ? 0 : 1;
 }
 
+static size_t get_sys_value(const char *source)
+{
+	FILE *f;
+	size_t v;
+
+	f = fopen(source, "r");
+	if (f == NULL) {
+		return (size_t)-1;
+	}
+
+	if (fscanf(f, "%zu", &v) != 1) {
+		fclose(f);
+		return (size_t)-1;
+	}
+
+	fclose(f);
+
+	return v;
+}
+
 #define stat_sizet_field(name, stype, sfield)                           \
 	{ (name), &read_common_sizet, (ptrdiff_t)offsetof(stype, sfield) }
 
@@ -294,14 +314,31 @@ int oscap_sys_memusage(struct sys_memusage *mu)
 	if (mu == NULL)
 		return -1;
 #if defined(OS_LINUX)
-	if (read_status(MEMUSAGE_LINUX_SYS_STATUS,
-	                mu, __sys_stat_ptable,
-	                (sizeof __sys_stat_ptable)/sizeof(struct stat_parser)) != 0)
-	{
-		return -1;
+	// cgroup
+	size_t cgroup_memory_usage = get_sys_value(MEMUSAGE_LINUX_SYS_CGROUP_USAGE);
+	size_t cgroup_memory_limit = get_sys_value(MEMUSAGE_LINUX_SYS_CGROUP_LIMIT);
+	if (cgroup_memory_usage != (size_t)-1 && cgroup_memory_limit != (size_t)-1) {
+		mu->mu_total = BYTES_TO_KIB(cgroup_memory_limit);
+		mu->mu_realfree = BYTES_TO_KIB(cgroup_memory_limit) - BYTES_TO_KIB(cgroup_memory_usage);
+	} else {
+		// cgroup2
+		size_t cgroup_memory_current = get_sys_value(MEMUSAGE_LINUX_SYS_CGROUP2_CURRENT);
+		size_t cgroup_memory_max = get_sys_value(MEMUSAGE_LINUX_SYS_CGROUP2_MAX);
+		if (cgroup_memory_current != (size_t)-1 && cgroup_memory_max != (size_t)-1) {
+			mu->mu_total = BYTES_TO_KIB(cgroup_memory_max);
+			mu->mu_realfree = BYTES_TO_KIB(cgroup_memory_max) - BYTES_TO_KIB(cgroup_memory_current);
+		} else {
+				if (read_status(MEMUSAGE_LINUX_SYS_STATUS,
+                                    mu, __sys_stat_ptable,
+                                    (sizeof __sys_stat_ptable)/sizeof(struct stat_parser)) != 0)
+				{
+					return -1;
+				}
+
+				mu->mu_realfree = mu->mu_free + mu->mu_cached + mu->mu_buffers;
+		}
 	}
 
-	mu->mu_realfree = mu->mu_free + mu->mu_cached + mu->mu_buffers;
 #elif defined(OS_FREEBSD)
 	if (freebsd_sys_memusage(mu))
 		return -1;

src/common/memusage.h

@@ -8,6 +8,11 @@
 # define MEMUSAGE_LINUX_PROC_ENV    "MEMUSAGE_PROC_STATUS"
 # define MEMUSAGE_LINUX_SYS_STATUS "/proc/meminfo"
 # define MEMUSAGE_LINUX_SYS_ENV "MEMUSAGE_SYS_STATUS"
+# define MEMUSAGE_LINUX_SYS_CGROUP_USAGE "/sys/fs/cgroup/memory/memory.usage_in_bytes"
+# define MEMUSAGE_LINUX_SYS_CGROUP_LIMIT "/sys/fs/cgroup/memory/memory.limit_in_bytes"
+# define MEMUSAGE_LINUX_SYS_CGROUP2_CURRENT "/sys/fs/cgroup/memory.current"
+# define MEMUSAGE_LINUX_SYS_CGROUP2_MAX "/sys/fs/cgroup/memory.max"
+
 #endif /* OS_LINUX */
 
 struct proc_memusage {