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[PATCH] virtiofsd: jail lo->proc_self_fd
From: |
Miklos Szeredi |
Subject: |
[PATCH] virtiofsd: jail lo->proc_self_fd |
Date: |
Wed, 29 Apr 2020 14:47:33 +0200 |
While it's not possible to escape the proc filesystem through
lo->proc_self_fd, it is possible to escape to the root of the proc
filesystem itself through "../..".
Use a temporary mount for opening lo->proc_self_fd, that has it's root at
/proc/self/fd/, preventing access to the ancestor directories.
Signed-off-by: Miklos Szeredi <address@hidden>
---
tools/virtiofsd/passthrough_ll.c | 27 +++++++++++++++++++++++++--
1 file changed, 25 insertions(+), 2 deletions(-)
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 4c35c95b256c..bc9c44c760f4 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -2536,6 +2536,8 @@ static void print_capabilities(void)
static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
{
pid_t child;
+ char template[] = "virtiofsd-XXXXXX";
+ char *tmpdir;
/*
* Create a new pid namespace for *child* processes. We'll have to
@@ -2597,12 +2599,33 @@ static void setup_namespaces(struct lo_data *lo, struct
fuse_session *se)
exit(1);
}
+ tmpdir = mkdtemp(template);
+ if (!tmpdir) {
+ fuse_log(FUSE_LOG_ERR, "tmpdir(%s): %m\n", template);
+ exit(1);
+ }
+
+ if (mount("/proc/self/fd", tmpdir, NULL, MS_BIND, NULL) < 0) {
+ fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, %s, MS_BIND): %m\n",
+ tmpdir);
+ exit(1);
+ }
+
/* Now we can get our /proc/self/fd directory file descriptor */
- lo->proc_self_fd = open("/proc/self/fd", O_PATH);
+ lo->proc_self_fd = open(tmpdir, O_PATH);
if (lo->proc_self_fd == -1) {
- fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
+ fuse_log(FUSE_LOG_ERR, "open(%s, O_PATH): %m\n", tmpdir);
exit(1);
}
+
+ if (umount2(tmpdir, MNT_DETACH) < 0) {
+ fuse_log(FUSE_LOG_ERR, "umount2(%s, MNT_DETACH): %m\n", tmpdir);
+ exit(1);
+ }
+
+ if (rmdir(tmpdir) < 0) {
+ fuse_log(FUSE_LOG_ERR, "rmdir(%s): %m\n", tmpdir);
+ }
}
/*
--
2.21.1