Description: Disable the Linux kernel's OOM-killer for the sshd parent
Author: Vaclav Ovsik <vaclav.ovsik@i.cz>
Author: Colin Watson <cjwatson@debian.org>
Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1470
Bug-Debian: http://bugs.debian.org/480020
Last-Update: 2010-02-27

Index: b/config.h.in
===================================================================
--- a/config.h.in
+++ b/config.h.in
@@ -1238,6 +1238,9 @@
 /* Define if X11 doesn't support AF_UNIX sockets on that system */
 #undef NO_X11_UNIX_SOCKETS
 
+/* Adjust Linux out-of-memory killer */
+#undef OOM_ADJUST
+
 /* Define if EVP_DigestUpdate returns void */
 #undef OPENSSL_EVP_DIGESTUPDATE_VOID
 
Index: b/configure
===================================================================
--- a/configure
+++ b/configure
@@ -8369,6 +8369,11 @@
 _ACEOF
 
 	fi
+
+cat >>confdefs.h <<\_ACEOF
+#define OOM_ADJUST 1
+_ACEOF
+
 	;;
 mips-sony-bsd|mips-sony-newsos4)
 
Index: b/configure.ac
===================================================================
--- a/configure.ac
+++ b/configure.ac
@@ -630,6 +630,7 @@
 		AC_DEFINE(SSH_TUN_PREPEND_AF, 1,
 		    [Prepend the address family to IP tunnel traffic])
 	fi
+	AC_DEFINE(OOM_ADJUST, 1, [Adjust Linux out-of-memory killer])
 	;;
 mips-sony-bsd|mips-sony-newsos4)
 	AC_DEFINE(NEED_SETPGRP, 1, [Need setpgrp to acquire controlling tty])
Index: b/openbsd-compat/port-linux.c
===================================================================
--- a/openbsd-compat/port-linux.c
+++ b/openbsd-compat/port-linux.c
@@ -18,7 +18,7 @@
  */
 
 /*
- * Linux-specific portability code - just SELinux support at present
+ * Linux-specific portability code
  */
 
 #include "includes.h"
@@ -27,6 +27,15 @@
 #include <stdarg.h>
 #include <string.h>
 
+#ifdef OOM_ADJUST
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#endif
+
+#include "log.h"
+
 #ifdef WITH_SELINUX
 #include "key.h"
 #include "hostfile.h"
@@ -34,7 +43,6 @@
 #ifdef HAVE_GETSEUSERBYNAME
 #include "xmalloc.h"
 #endif
-#include "log.h"
 #include "port-linux.h"
 
 #include <selinux/selinux.h>
@@ -186,3 +194,47 @@
 	debug3("%s: done", __func__);
 }
 #endif /* WITH_SELINUX */
+
+#ifdef OOM_ADJUST
+/* Get the out-of-memory adjustment file for the current process */
+static int
+oom_adj_open(int oflag)
+{
+	int fd = open("/proc/self/oom_adj", oflag);
+	if (fd < 0)
+		logit("error opening /proc/self/oom_adj: %s", strerror(errno));
+	return fd;
+}
+
+/* Get the current OOM adjustment */
+int
+oom_adj_get(char *buf, size_t maxlen)
+{
+	ssize_t n;
+	int fd = oom_adj_open(O_RDONLY);
+	if (fd < 0)
+		return -1;
+	n = read(fd, buf, maxlen);
+	if (n < 0)
+		logit("error reading /proc/self/oom_adj: %s", strerror(errno));
+	else
+		buf[n] = '\0';
+	close(fd);
+	return n < 0 ? -1 : 0;
+}
+
+/* Set the current OOM adjustment */
+int
+oom_adj_set(const char *buf)
+{
+	ssize_t n;
+	int fd = oom_adj_open(O_WRONLY);
+	if (fd < 0)
+		return -1;
+	n = write(fd, buf, strlen(buf));
+	if (n < 0)
+		logit("error writing /proc/self/oom_adj: %s", strerror(errno));
+	close(fd);
+	return n < 0 ? -1 : 0;
+}
+#endif
Index: b/openbsd-compat/port-linux.h
===================================================================
--- a/openbsd-compat/port-linux.h
+++ b/openbsd-compat/port-linux.h
@@ -25,4 +25,9 @@
 void ssh_selinux_setup_exec_context(char *);
 #endif
 
+#ifdef OOM_ADJUST
+int oom_adj_get(char *buf, size_t maxlen);
+int oom_adj_set(const char *buf);
+#endif
+
 #endif /* ! _PORT_LINUX_H */
Index: b/sshd.c
===================================================================
--- a/sshd.c
+++ b/sshd.c
@@ -254,6 +254,11 @@
 /* Unprivileged user */
 struct passwd *privsep_pw = NULL;
 
+#ifdef OOM_ADJUST
+/* Linux out-of-memory killer adjustment */
+static char oom_adj_save[8];
+#endif
+
 /* Prototypes for various functions defined later in this file. */
 void destroy_sensitive_data(void);
 void demote_sensitive_data(void);
@@ -908,6 +913,31 @@
 	debug3("%s: done", __func__);
 }
 
+#ifdef OOM_ADJUST
+/*
+ * If requested in the environment, tell the Linux kernel's out-of-memory
+ * killer to avoid sshd. The old state will be restored when forking child
+ * processes.
+ */
+static void
+oom_adjust_startup(void)
+{
+	const char *oom_adj = getenv("SSHD_OOM_ADJUST");
+
+	if (!oom_adj || !*oom_adj)
+		return;
+	oom_adj_get(oom_adj_save, sizeof(oom_adj_save));
+	oom_adj_set(oom_adj);
+}
+
+static void
+oom_restore(void)
+{
+	if (oom_adj_save[0])
+		oom_adj_set(oom_adj_save);
+}
+#endif
+
 /* Accept a connection from inetd */
 static void
 server_accept_inetd(int *sock_in, int *sock_out)
@@ -1670,6 +1700,11 @@
 	/* ignore SIGPIPE */
 	signal(SIGPIPE, SIG_IGN);
 
+#ifdef OOM_ADJUST
+	/* Adjust out-of-memory killer */
+	oom_adjust_startup();
+#endif
+
 	/* Get a connection, either from inetd or a listening TCP socket */
 	if (inetd_flag) {
 		server_accept_inetd(&sock_in, &sock_out);
@@ -1708,6 +1743,10 @@
 	/* This is the child processing a new connection. */
 	setproctitle("%s", "[accepted]");
 
+#ifdef OOM_ADJUST
+	oom_restore();
+#endif
+
 	/*
 	 * Create a new session and process group since the 4.4BSD
 	 * setlogin() affects the entire process group.  We don't