linux-kernel - [RFC PATCH 3/3] proc: hide unknown groups in status

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Date:   Mon, 10 May 2021 15:00:11 +0200
From:   Giuseppe Scrivano <gscrivan@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     serge@...lyn.com, dwalsh@...hat.com, christian.brauner@...ntu.com,
        ebiederm@...ssion.com
Subject: [RFC PATCH 3/3] proc: hide unknown groups in status

when the "shadow" mode is enabled for the user namespace, do not copy
to userspace the groups that are not mapped.

Signed-off-by: Giuseppe Scrivano <gscrivan@...hat.com>
---
 fs/proc/array.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 7ec59171f197..81dc733773d4 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -202,9 +202,17 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 
 	seq_puts(m, "\nGroups:\t");
 	group_info = cred->group_info;
-	for (g = 0; g < group_info->ngroups; g++)
+	for (g = 0; g < group_info->ngroups; g++) {
+		gid_t gid = from_kgid(user_ns, group_info->gid[g]);
+
+		if (gid == (gid_t)-1) {
+			if (user_ns->flags & USERNS_SETGROUPS_SHADOW)
+				continue;
+			gid = overflowgid;
+		}
 		seq_put_decimal_ull(m, g ? " " : "",
-				from_kgid_munged(user_ns, group_info->gid[g]));
+				gid);
+	}
 	put_cred(cred);
 	/* Trailing space shouldn't have been added in the first place. */
 	seq_putc(m, ' ');
-- 
2.31.1