commit 54b501992dd2a839e94e76aa392c392b55080ce8
author Kees Cook <keescook@chromium.org> Mon Jul 30 14:39:18 2012 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Mon Jul 30 17:25:11 2012 -0700
tree 6d174fb95516f01e385d31d5ef87a248d8740fd2
parent 9520628e8ceb69fa9a4aee6b57f22675d9e1b709

coredump: warn about unsafe suid_dumpable / core_pattern combo

When suid_dumpable=2, detect unsafe core_pattern settings and warn when
they are seen.

Signed-off-by: Kees Cook <keescook@chromium.org>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alan Cox <alan@linux.intel.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: James Morris <james.l.morris@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sysctl.c

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4ab1187..b46f496 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -174,6 +174,11 @@
 				void __user *buffer, size_t *lenp, loff_t *ppos);
 #endif
 
+static int proc_dointvec_minmax_coredump(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp, loff_t *ppos);
+static int proc_dostring_coredump(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp, loff_t *ppos);
+
 #ifdef CONFIG_MAGIC_SYSRQ
 /* Note: sysrq code uses it's own private copy */
 static int __sysrq_enabled = SYSRQ_DEFAULT_ENABLE;
@@ -410,7 +415,7 @@
 		.data		= core_pattern,
 		.maxlen		= CORENAME_MAX_SIZE,
 		.mode		= 0644,
-		.proc_handler	= proc_dostring,
+		.proc_handler	= proc_dostring_coredump,
 	},
 	{
 		.procname	= "core_pipe_limit",
@@ -1498,7 +1503,7 @@
 		.data		= &suid_dumpable,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
+		.proc_handler	= proc_dointvec_minmax_coredump,
 		.extra1		= &zero,
 		.extra2		= &two,
 	},
@@ -2009,6 +2014,34 @@
 				do_proc_dointvec_minmax_conv, &param);
 }
 
+static void validate_coredump_safety(void)
+{
+	if (suid_dumpable == SUID_DUMPABLE_SAFE &&
+	    core_pattern[0] != '/' && core_pattern[0] != '|') {
+		printk(KERN_WARNING "Unsafe core_pattern used with "\
+			"suid_dumpable=2. Pipe handler or fully qualified "\
+			"core dump path required.\n");
+	}
+}
+
+static int proc_dointvec_minmax_coredump(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	int error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	if (!error)
+		validate_coredump_safety();
+	return error;
+}
+
+static int proc_dostring_coredump(struct ctl_table *table, int write,
+		  void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	int error = proc_dostring(table, write, buffer, lenp, ppos);
+	if (!error)
+		validate_coredump_safety();
+	return error;
+}
+
 static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int write,
 				     void __user *buffer,
 				     size_t *lenp, loff_t *ppos,