From fd2d830ad82595c97afd2c453788c9ccc5fa2182 Mon Sep 17 00:00:00 2001
From: dtucker <dtucker>
Date: Tue, 8 Dec 2009 02:39:48 +0000
Subject: [PATCH]  - (dtucker) Bug #1470: Disable OOM-killing of the listening
 sshd on Linux,    based on a patch from Vaclav Ovsik and Colin Watson.  ok
 djm.

---
 ChangeLog                   |  4 +++
 configure.ac                |  1 +
 openbsd-compat/port-linux.c | 61 ++++++++++++++++++++++++++++++++++++-
 openbsd-compat/port-linux.h |  5 +++
 platform.c                  | 12 ++++++++
 platform.h                  |  1 +
 sshd.c                      |  1 +
 7 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 53d89c90..7f95697f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+20091208
+ - (dtucker) Bug #1470: Disable OOM-killing of the listening sshd on Linux,
+   based on a patch from Vaclav Ovsik and Colin Watson.  ok djm.
+
 20091207
  - (dtucker) Bug #1160: use pkg-config for opensc config if it's available.
    Tested by Martin Paljak.
diff --git a/configure.ac b/configure.ac
index 2de30f33..71b313c5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -589,6 +589,7 @@ main() { if (NSVersionOfRunTimeLibrary("System") >= (60 << 16))
 		if it doesn't return EOPNOTSUPP.])
 	AC_DEFINE(_PATH_BTMP, "/var/log/btmp", [log for bad login attempts])
 	AC_DEFINE(USE_BTMP)
+	AC_DEFINE(LINUX_OOM_ADJUST, 1, [Adjust Linux out-of-memory killer])
 	inet6_default_4in6=yes
 	case `uname -r` in
 	1.*|2.0.*)
diff --git a/openbsd-compat/port-linux.c b/openbsd-compat/port-linux.c
index eea6b19b..2f380724 100644
--- a/openbsd-compat/port-linux.c
+++ b/openbsd-compat/port-linux.c
@@ -23,15 +23,17 @@
 
 #include "includes.h"
 
+#if defined(WITH_SELINUX) || defined(LINUX_OOM_ADJUST)
 #include <errno.h>
 #include <stdarg.h>
 #include <string.h>
+#include <stdio.h>
 
-#ifdef WITH_SELINUX
 #include "log.h"
 #include "xmalloc.h"
 #include "port-linux.h"
 
+#ifdef WITH_SELINUX
 #include <selinux/selinux.h>
 #include <selinux/flask.h>
 #include <selinux/get_context_list.h>
@@ -204,3 +206,60 @@ ssh_selinux_change_context(const char *newname)
 	xfree(newctx);
 }
 #endif /* WITH_SELINUX */
+
+#ifdef LINUX_OOM_ADJUST
+#define OOM_ADJ_PATH	"/proc/self/oom_adj"
+/*
+ * The magic "don't kill me", as documented in eg:
+ * http://lxr.linux.no/#linux+v2.6.32/Documentation/filesystems/proc.txt
+ */
+#define OOM_ADJ_NOKILL	-17
+
+static int oom_adj_save = INT_MIN;
+
+/*
+ * Tell the kernel's out-of-memory killer to avoid sshd.
+ * Returns the previous oom_adj value or zero.
+ */
+void
+oom_adjust_setup(void)
+{
+	FILE *fp;
+
+	debug3("%s", __func__);
+	if ((fp = fopen(OOM_ADJ_PATH, "r+")) != NULL) {
+		if (fscanf(fp, "%d", &oom_adj_save) != 1)
+			logit("error reading %s: %s", OOM_ADJ_PATH, strerror(errno));
+		else {
+			rewind(fp);
+			if (fprintf(fp, "%d\n", OOM_ADJ_NOKILL) <= 0)
+				logit("error writing %s: %s",
+				    OOM_ADJ_PATH, strerror(errno));
+			else
+				verbose("Set %s from %d to %d",
+				    OOM_ADJ_PATH, oom_adj_save, OOM_ADJ_NOKILL);
+		}
+		fclose(fp);
+	}
+}
+
+/* Restore the saved OOM adjustment */
+void
+oom_adjust_restore(void)
+{
+	FILE *fp;
+
+	debug3("%s", __func__);
+	if (oom_adj_save == INT_MIN || (fp = fopen(OOM_ADJ_PATH, "w")) == NULL)
+		return;
+
+	if (fprintf(fp, "%d\n", oom_adj_save) <= 0)
+		logit("error writing %s: %s", OOM_ADJ_PATH, strerror(errno));
+	else
+		verbose("Set %s to %d", OOM_ADJ_PATH, oom_adj_save);
+
+	fclose(fp);
+	return;
+}
+#endif /* LINUX_OOM_ADJUST */
+#endif /* WITH_SELINUX || LINUX_OOM_ADJUST */
diff --git a/openbsd-compat/port-linux.h b/openbsd-compat/port-linux.h
index 6b59d84b..7e087c75 100644
--- a/openbsd-compat/port-linux.h
+++ b/openbsd-compat/port-linux.h
@@ -26,4 +26,9 @@ void ssh_selinux_setup_exec_context(char *);
 void ssh_selinux_change_context(const char *);
 #endif
 
+#ifdef LINUX_OOM_ADJUST
+void oom_adjust_restore(void);
+void oom_adjust_setup(void);
+#endif
+
 #endif /* ! _PORT_LINUX_H */
diff --git a/platform.c b/platform.c
index abfa9f1b..5d728a51 100644
--- a/platform.c
+++ b/platform.c
@@ -21,6 +21,15 @@
 
 #include "openbsd-compat/openbsd-compat.h"
 
+void
+platform_pre_listen(void)
+{
+#ifdef LINUX_OOM_ADJUST
+	/* Adjust out-of-memory killer so listening process is not killed */
+	oom_adjust_setup();
+#endif
+}
+
 void
 platform_pre_fork(void)
 {
@@ -43,4 +52,7 @@ platform_post_fork_child(void)
 #ifdef USE_SOLARIS_PROCESS_CONTRACTS
 	solaris_contract_post_fork_child();
 #endif
+#ifdef LINUX_OOM_ADJUST
+	oom_adjust_restore();
+#endif
 }
diff --git a/platform.h b/platform.h
index 47e6aad7..2d48c8ca 100644
--- a/platform.h
+++ b/platform.h
@@ -18,6 +18,7 @@
 
 #include <sys/types.h>
 
+void platform_pre_listen(void);
 void platform_pre_fork(void);
 void platform_post_fork_parent(pid_t child_pid);
 void platform_post_fork_child(void);
diff --git a/sshd.c b/sshd.c
index 04d8f9fa..38aaa182 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1656,6 +1656,7 @@ main(int ac, char **av)
 	if (inetd_flag) {
 		server_accept_inetd(&sock_in, &sock_out);
 	} else {
+		platform_pre_listen();
 		server_listen();
 
 		if (options.protocol & SSH_PROTO_1)
-- 
2.45.1