From 5138a20765c76cdc8f245d3d7caeffe9a9011bb2 Mon Sep 17 00:00:00 2001 From: Kyle Evans Date: Thu, 24 Jul 2025 09:59:07 -0500 Subject: [PATCH] tftpd: explicitly set egid after dropping supplemental groups tftpd seems to be the last program in base that implicitly relies on setgroups() to set the egid. This is a security landmine in portable software as most operating systems don't behave this way, so do an explicit setgid() in case the kernel doesn't set it already. While we're here, FreeBSD's setgroups() has supported nominally clearing all supplemental groups since 1997. It still leaves the egid in our cr_groups[0] because we don't have an out-of-band way to store the egid, and on other systems it'll clear the supplemental group entirely as one would want. Reviewed by: allanjude (previous version), des, olce Differential Revision: https://reviews.freebsd.org/D51149 --- libexec/tftpd/tftpd.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/libexec/tftpd/tftpd.c b/libexec/tftpd/tftpd.c index f8f9bd549a2..a3faee86e7d 100644 --- a/libexec/tftpd/tftpd.c +++ b/libexec/tftpd/tftpd.c @@ -351,10 +351,14 @@ main(int argc, char *argv[]) tftp_log(LOG_ERR, "chdir: %s", strerror(errno)); exit(1); } - if (setgroups(1, &nobody->pw_gid) != 0) { + if (setgroups(0, NULL) != 0) { tftp_log(LOG_ERR, "setgroups failed"); exit(1); } + if (setgid(nobody->pw_gid) != 0) { + tftp_log(LOG_ERR, "setgid failed"); + exit(1); + } if (setuid(nobody->pw_uid) != 0) { tftp_log(LOG_ERR, "setuid failed"); exit(1);