[lxc-devel] [lxc/master] conf: copy mountinfo for remount_all_slave()
brauner on Github
lxc-bot at linuxcontainers.org
Mon Jun 4 10:52:47 UTC 2018
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From 918c8bdb2dc278528ddb7b2d043979c172ea6e93 Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian.brauner at ubuntu.com>
Date: Mon, 4 Jun 2018 12:49:05 +0200
Subject: [PATCH] conf: copy mountinfo for remount_all_slave()
While a container reads mountinfo from proc fs, the mountinfo can be changed by
the kernel anytime. This has caused critical issues on some devices.
Signed-off-by: Donghwa Jeong dh48.jeong at samsung.com
Reported-by: Donghwa Jeong dh48.jeong at samsung.com
Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
---
src/lxc/conf.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 47 insertions(+), 3 deletions(-)
diff --git a/src/lxc/conf.c b/src/lxc/conf.c
index 05d58081e..f16fdaf50 100644
--- a/src/lxc/conf.c
+++ b/src/lxc/conf.c
@@ -43,6 +43,7 @@
#include <sys/mount.h>
#include <sys/param.h>
#include <sys/prctl.h>
+#include <sys/sendfile.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/syscall.h>
@@ -3178,14 +3179,56 @@ void tmp_proc_unmount(struct lxc_conf *lxc_conf)
/* Walk /proc/mounts and change any shared entries to slave. */
void remount_all_slave(void)
{
+ int memfd, mntinfo_fd;
+ ssize_t copied;
FILE *f;
size_t len = 0;
char *line = NULL;
- f = fopen("/proc/self/mountinfo", "r");
+ mntinfo_fd = open("/proc/self/mountinfo", O_RDONLY | O_CLOEXEC);
+ if (mntinfo_fd < 0)
+ return;
+
+ memfd = memfd_create(".lxc_mountinfo", MFD_CLOEXEC);
+ if (memfd < 0) {
+ char template[] = P_tmpdir "/.lxc_mountinfo_XXXXXX";
+
+ if (errno != ENOSYS) {
+ close(mntinfo_fd);
+ WARN("Failed to create temporary in-memory file");
+ return;
+ }
+
+ memfd = lxc_make_tmpfile(template, true);
+ }
+ if (memfd < 0) {
+ close(mntinfo_fd);
+ WARN("Failed to create temporary file");
+ return;
+ }
+
+#define __LXC_SENDFILE_MAX 0x7ffff000 /* maximum number of bytes sendfile can handle */
+again:
+ copied = sendfile(memfd, mntinfo_fd, NULL, __LXC_SENDFILE_MAX);
+ if (copied < 0) {
+ if (errno == EINTR)
+ goto again;
+
+ close(mntinfo_fd);
+ close(memfd);
+ WARN("Failed to copy \"/proc/self/mountinfo\"");
+ return;
+ }
+ close(mntinfo_fd);
+
+ /* After a successful fdopen() memfd will be closed when calling
+ * fclose(f). Calling close(memfd) afterwards is undefined.
+ */
+ f = fdopen(memfd, "r");
if (!f) {
- SYSERROR("Failed to open \"/proc/self/mountinfo\" to mark all shared");
- ERROR("Continuing container startup...");
+ WARN("Failed to open copy of \"/proc/self/mountinfo\" to mark "
+ "all shared. Continuing");
+ close(memfd);
return;
}
@@ -3214,6 +3257,7 @@ void remount_all_slave(void)
}
fclose(f);
free(line);
+ TRACE("Remounted all mount table entries as MS_SLAVE");
}
static int lxc_execute_bind_init(struct lxc_handler *handler)
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