From 449e8171f96a6a944d1f3b7d3627ae059eae21ca Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Tue, 25 Jan 2022 13:51:14 -0500 Subject: virtiofsd: Drop membership of all supplementary groups (CVE-2022-0358) 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 Suggested-by: Miklos Szeredi Reviewed-by: Stefan Hajnoczi Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Vivek Goyal Message-Id: Signed-off-by: Dr. David Alan Gilbert dgilbert: Fixed missing {}'s style nit --- 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 64b5b4fbb1..b3d0674f6d 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -54,6 +54,7 @@ #include #include #include +#include #include "qemu/cutils.h" #include "passthrough_helpers.h" @@ -1161,6 +1162,30 @@ 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. @@ -3926,6 +3951,8 @@ int main(int argc, char *argv[]) qemu_init_exec_dir(argv[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; -- cgit v1.2.3