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From 2754dc2c7def01d7dd1bb39f3e86ef444652d397 Mon Sep 17 00:00:00 2001
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From: Vivek Goyal <vgoyal@redhat.com>
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Date: Tue, 25 Jan 2022 13:51:14 -0500
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Subject: [PATCH 1/6] virtiofsd: Drop membership of all supplementary groups
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(CVE-2022-0358)
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RH-Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
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RH-MergeRequest: 102: virtiofsd: Drop membership of all supplementary groups (CVE-2022-0358)
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RH-Commit: [1/1] 93e56c88277fec8e42559a899d32b80fac4a923f
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RH-Bugzilla: 2046198
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RH-Acked-by: Greg Kurz <gkurz@redhat.com>
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RH-Acked-by: Sergio Lopez <None>
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RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
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At the start, drop membership of all supplementary groups. This is
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not required.
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If we have membership of "root" supplementary group and when we switch
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uid/gid using setresuid/setsgid, we still retain membership of existing
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supplemntary groups. And that can allow some operations which are not
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normally allowed.
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For example, if root in guest creates a dir as follows.
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$ mkdir -m 03777 test_dir
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This sets SGID on dir as well as allows unprivileged users to write into
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this dir.
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And now as unprivileged user open file as follows.
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$ su test
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$ fd = open("test_dir/priviledge_id", O_RDWR|O_CREAT|O_EXCL, 02755);
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This will create SGID set executable in test_dir/.
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And that's a problem because now an unpriviliged user can execute it,
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get egid=0 and get access to resources owned by "root" group. This is
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privilege escalation.
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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2044863
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Fixes: CVE-2022-0358
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Reported-by: JIETAO XIAO <shawtao1125@gmail.com>
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Suggested-by: Miklos Szeredi <mszeredi@redhat.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
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Message-Id: <YfBGoriS38eBQrAb@redhat.com>
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Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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dgilbert: Fixed missing {}'s style nit
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(cherry picked from commit 449e8171f96a6a944d1f3b7d3627ae059eae21ca)
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---
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tools/virtiofsd/passthrough_ll.c | 27 +++++++++++++++++++++++++++
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1 file changed, 27 insertions(+)
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diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
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index 64b5b4fbb1..b3d0674f6d 100644
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--- a/tools/virtiofsd/passthrough_ll.c
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+++ b/tools/virtiofsd/passthrough_ll.c
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@@ -54,6 +54,7 @@
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#include <sys/wait.h>
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#include <sys/xattr.h>
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#include <syslog.h>
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+#include <grp.h>
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#include "qemu/cutils.h"
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#include "passthrough_helpers.h"
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@@ -1161,6 +1162,30 @@ static void lo_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
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#define OURSYS_setresuid SYS_setresuid
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#endif
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+static void drop_supplementary_groups(void)
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+{
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+ int ret;
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+
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+ ret = getgroups(0, NULL);
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+ if (ret == -1) {
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+ fuse_log(FUSE_LOG_ERR, "getgroups() failed with error=%d:%s\n",
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+ errno, strerror(errno));
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+ exit(1);
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+ }
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+
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+ if (!ret) {
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+ return;
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+ }
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+
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+ /* Drop all supplementary groups. We should not need it */
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+ ret = setgroups(0, NULL);
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+ if (ret == -1) {
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+ fuse_log(FUSE_LOG_ERR, "setgroups() failed with error=%d:%s\n",
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+ errno, strerror(errno));
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+ exit(1);
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+ }
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+}
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+
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/*
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* Change to uid/gid of caller so that file is created with
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* ownership of caller.
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@@ -3926,6 +3951,8 @@ int main(int argc, char *argv[])
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qemu_init_exec_dir(argv[0]);
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+ drop_supplementary_groups();
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+
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pthread_mutex_init(&lo.mutex, NULL);
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lo.inodes = g_hash_table_new(lo_key_hash, lo_key_equal);
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lo.root.fd = -1;
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--
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2.27.0
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