linux-kernel - [PATCH 3.16.y-ckt 129/216] userns: Unbreak the unprivileged remount tests

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Message-Id: <1421087394-2712-17-git-send-email-luis.henriques@canonical.com>
Date:	Mon, 12 Jan 2015 18:28:27 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 129/216] userns: Unbreak the unprivileged remount tests

3.16.7-ckt4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@...ssion.com>

commit db86da7cb76f797a1a8b445166a15cb922c6ff85 upstream.

A security fix in caused the way the unprivileged remount tests were
using user namespaces to break.  Tweak the way user namespaces are
being used so the test works again.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 .../selftests/mount/unprivileged-remount-test.c    | 32 ++++++++++++++++------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/mount/unprivileged-remount-test.c b/tools/testing/selftests/mount/unprivileged-remount-test.c
index 9669d375625a..517785052f1c 100644
--- a/tools/testing/selftests/mount/unprivileged-remount-test.c
+++ b/tools/testing/selftests/mount/unprivileged-remount-test.c
@@ -53,17 +53,14 @@ static void die(char *fmt, ...)
 	exit(EXIT_FAILURE);
 }
 
-static void write_file(char *filename, char *fmt, ...)
+static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt, va_list ap)
 {
 	char buf[4096];
 	int fd;
 	ssize_t written;
 	int buf_len;
-	va_list ap;
 
-	va_start(ap, fmt);
 	buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
-	va_end(ap);
 	if (buf_len < 0) {
 		die("vsnprintf failed: %s\n",
 		    strerror(errno));
@@ -74,6 +71,8 @@ static void write_file(char *filename, char *fmt, ...)
 
 	fd = open(filename, O_WRONLY);
 	if (fd < 0) {
+		if ((errno == ENOENT) && enoent_ok)
+			return;
 		die("open of %s failed: %s\n",
 		    filename, strerror(errno));
 	}
@@ -92,6 +91,26 @@ static void write_file(char *filename, char *fmt, ...)
 	}
 }
 
+static void maybe_write_file(char *filename, char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vmaybe_write_file(true, filename, fmt, ap);
+	va_end(ap);
+
+}
+
+static void write_file(char *filename, char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vmaybe_write_file(false, filename, fmt, ap);
+	va_end(ap);
+
+}
+
 static int read_mnt_flags(const char *path)
 {
 	int ret;
@@ -144,13 +163,10 @@ static void create_and_enter_userns(void)
 			strerror(errno));
 	}
 
+	maybe_write_file("/proc/self/setgroups", "deny");
 	write_file("/proc/self/uid_map", "0 %d 1", uid);
 	write_file("/proc/self/gid_map", "0 %d 1", gid);
 
-	if (setgroups(0, NULL) != 0) {
-		die("setgroups failed: %s\n",
-			strerror(errno));
-	}
 	if (setgid(0) != 0) {
 		die ("setgid(0) failed %s\n",
 			strerror(errno));
-- 
2.1.4

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