[PATCH] getgroups.2: Document unprivileged setgroups calls

[Josh Triplett <josh@joshtriplett.org>]

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
---
v3: Document use of gid/egid/sgid.
v2: Document requirement for no_new_privs.

(If this doesn't end up going into 3.18, the version number in the patch will
need updating.)

 man2/getgroups.2 | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/man2/getgroups.2 b/man2/getgroups.2
index 373c204..e2b834e 100644
--- a/man2/getgroups.2
+++ b/man2/getgroups.2
@@ -81,9 +81,16 @@ to be used in a further call to
 .PP
 .BR setgroups ()
 sets the supplementary group IDs for the calling process.
-Appropriate privileges (Linux: the
+A process with the
 .B CAP_SETGID
-capability) are required.
+capability may change its supplementary group IDs arbitrarily.
+As of Linux 3.18, any process that has enabled PR_SET_NO_NEW_PRIVS (see
+.BR prctl (2))
+may drop supplementary groups, or add any of the current real UID, the current
+effective UID, or the current saved set-user-ID; adding any other group ID
+requires the
+.B CAP_SETGID
+capability.
 The
 .I size
 argument specifies the number of supplementary group IDs
-- 
2.1.3