[libvirt PATCH 12/17] util: Try to get limits from /proc
Calling prlimit() requires elevated privileges, specifically
CAP_SYS_RESOURCE, and getrlimit() only works for the current
process which is too limiting for our needs; /proc/$pid/limits,
on the other hand, can be read by any process, so implement
parsing that file as a fallback for when prlimit() fails.
This is useful in containerized environments.
Signed-off-by: Andrea Bolognani <abologna(a)redhat.com>
---
src/util/virprocess.c | 98 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 98 insertions(+)
diff --git a/src/util/virprocess.c b/src/util/virprocess.c
index abce522bf3..e62ec379a6 100644
--- a/src/util/virprocess.c
+++ b/src/util/virprocess.c
@@ -757,6 +757,95 @@ virProcessSetRLimit(int resource,
#endif /* WITH_SETRLIMIT */
#if WITH_GETRLIMIT
+static const char*
+virProcessLimitResourceToLabel(int resource)
+{
+ switch (resource) {
+# if defined(RLIMIT_MEMLOCK)
+ case RLIMIT_MEMLOCK:
+ return "Max locked memory";
+# endif /* defined(RLIMIT_MEMLOCK) */
+
+# if defined(RLIMIT_NPROC)
+ case RLIMIT_NPROC:
+ return "Max processes";
+# endif /* defined(RLIMIT_NPROC) */
+
+# if defined(RLIMIT_NOFILE)
+ case RLIMIT_NOFILE:
+ return "Max open files";
+# endif /* defined(RLIMIT_NOFILE) */
+
+# if defined(RLIMIT_CORE)
+ case RLIMIT_CORE:
+ return "Max core file size";
+# endif /* defined(RLIMIT_CORE) */
+
+ default:
+ return NULL;
+ }
+}
+
+static int
+virProcessGetLimitFromProc(pid_t pid,
+ int resource,
+ struct rlimit *limit)
+{
+ g_autofree char *procfile = NULL;
+ g_autofree char *buf = NULL;
+ g_auto(GStrv) lines = NULL;
+ const char *label;
+ size_t len;
+ size_t i;
+
+ if (!(label = virProcessLimitResourceToLabel(resource))) {
+ virReportError(VIR_ERR_INTERNAL_ERROR,
+ _("Unknown resource %d requested for process %lld"),
+ resource, (long long)pid);
+ return -1;
+ }
+
+ procfile = g_strdup_printf("/proc/%lld/limits", (long long)pid);
+
+ if (!g_file_get_contents(procfile, &buf, &len, NULL))
+ return -1;
+
+ if (!(lines = g_strsplit(buf, "\n", 0)))
+ return -1;
+
+ for (i = 0; lines[i]; i++) {
+ g_autofree char *softLimit = NULL;
+ g_autofree char *hardLimit = NULL;
+ char *line = lines[i];
+ unsigned long long tmp;
+
+ if (!STRPREFIX(line, label))
+ continue;
+
+ line += strlen(label);
+
+ if (sscanf(line, "%ms %ms %*s", &softLimit, &hardLimit) <
2)
+ return -1;
+
+ if (STREQ(softLimit, "unlimited")) {
+ limit->rlim_cur = RLIM_INFINITY;
+ } else {
+ if (virStrToLong_ull(softLimit, NULL, 10, &tmp) < 0)
+ return -1;
+ limit->rlim_cur = tmp;
+ }
+ if (STREQ(hardLimit, "unlimited")) {
+ limit->rlim_max = RLIM_INFINITY;
+ } else {
+ if (virStrToLong_ull(hardLimit, NULL, 10, &tmp) < 0)
+ return -1;
+ limit->rlim_max = tmp;
+ }
+ }
+
+ return 0;
+}
+
static int
virProcessGetLimit(pid_t pid,
int resource,
@@ -768,6 +857,15 @@ virProcessGetLimit(pid_t pid,
if (virProcessPrLimit(pid, resource, NULL, old_limit) == 0)
return 0;
+ /* For whatever reason, using prlimit() on another process - even
+ * when it's just to obtain the current limit rather than changing
+ * it - requires CAP_SYS_RESOURCE, which we might not have in a
+ * containerized environment; on the other hand, no particular
+ * permission is needed to poke around /proc, so try that if going
+ * through the syscall didn't work */
+ if (virProcessGetLimitFromProc(pid, resource, old_limit) == 0)
+ return 0;
+
if (same_process && virProcessGetRLimit(resource, old_limit) == 0)
return 0;
--
2.26.2