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From 746e07f2d54908296dde64e97e12ea33a35063e0 Mon Sep 17 00:00:00 2001
From: Vivek Goyal <vgoyal@redhat.com>
Date: Tue, 25 Jan 2022 13:51:14 -0500
Subject: [PATCH] virtiofsd: Drop membership of all supplementary groups
(CVE-2022-0358)
RH-Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
RH-MergeRequest: 106: 8.5.0z non-av; virtiofsd security fix - drop secondary groups
RH-Commit: [1/1] e39df0b31f3c236675262395b94d5c10e8e3073f
RH-Bugzilla: 2048627
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
RH-Acked-by: Vivek Goyal <None>
At the start, drop membership of all supplementary groups. This is
not required.
If we have membership of "root" supplementary group and when we switch
uid/gid using setresuid/setsgid, we still retain membership of existing
supplemntary groups. And that can allow some operations which are not
normally allowed.
For example, if root in guest creates a dir as follows.
$ mkdir -m 03777 test_dir
This sets SGID on dir as well as allows unprivileged users to write into
this dir.
And now as unprivileged user open file as follows.
$ su test
$ fd = open("test_dir/priviledge_id", O_RDWR|O_CREAT|O_EXCL, 02755);
This will create SGID set executable in test_dir/.
And that's a problem because now an unpriviliged user can execute it,
get egid=0 and get access to resources owned by "root" group. This is
privilege escalation.
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2044863
Fixes: CVE-2022-0358
Reported-by: JIETAO XIAO <shawtao1125@gmail.com>
Suggested-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Message-Id: <YfBGoriS38eBQrAb@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
dgilbert: Fixed missing {}'s style nit
(cherry picked from commit 449e8171f96a6a944d1f3b7d3627ae059eae21ca)
dgilbert: Minor fixup around #includes on backport
---
tools/virtiofsd/passthrough_ll.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index b47029da89..578131179c 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -63,6 +63,7 @@
#include <sys/xattr.h>
#include <syslog.h>
#include <unistd.h>
+#include <grp.h>
#include "passthrough_helpers.h"
#include "seccomp.h"
@@ -1058,6 +1059,30 @@ static void lo_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
#define OURSYS_setresuid SYS_setresuid
#endif
+static void drop_supplementary_groups(void)
+{
+ int ret;
+
+ ret = getgroups(0, NULL);
+ if (ret == -1) {
+ fuse_log(FUSE_LOG_ERR, "getgroups() failed with error=%d:%s\n",
+ errno, strerror(errno));
+ exit(1);
+ }
+
+ if (!ret) {
+ return;
+ }
+
+ /* Drop all supplementary groups. We should not need it */
+ ret = setgroups(0, NULL);
+ if (ret == -1) {
+ fuse_log(FUSE_LOG_ERR, "setgroups() failed with error=%d:%s\n",
+ errno, strerror(errno));
+ exit(1);
+ }
+}
+
/*
* Change to uid/gid of caller so that file is created with
* ownership of caller.
@@ -3010,6 +3035,8 @@ int main(int argc, char *argv[])
/* Don't mask creation mode, kernel already did that */
umask(0);
+ drop_supplementary_groups();
+
pthread_mutex_init(&lo.mutex, NULL);
lo.inodes = g_hash_table_new(lo_key_hash, lo_key_equal);
lo.root.fd = -1;
--
2.27.0