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From:   Alexey Gladkov <legion@kernel.org>
To:     LKML <linux-kernel@vger.kernel.org>,
        Linux Containers <containers@lists.linux.dev>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Christian Brauner <brauner@kernel.org>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Manfred Spraul <manfred@colorfullife.com>
Subject: [PATCH v1] sysctl: Allow change system v ipc sysctls inside ipc namespace
Date:   Tue, 12 Jul 2022 18:17:38 +0200
Message-Id: <54e6b6b1b430537748a7136e854923498443f78a.1657642613.git.legion@kernel.org>
MIME-Version: 1.0
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Rootless containers are not allowed to modify kernel IPC parameters such
as kernel.msgmnb.

It seems to me that we can allow customization of these parameters if
the user has CAP_SYS_RESOURCE in that ipc namespace.

CAP_SYS_RESOURCE is already needed in order to overcome mqueue limits
(msg_max and msgsize_max).

Signed-off-by: Alexey Gladkov <legion@kernel.org>
---
 ipc/ipc_sysctl.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index ef313ecfb53a..e79452867720 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -193,16 +193,19 @@ static int set_is_seen(struct ctl_table_set *set)
 static int ipc_permissions(struct ctl_table_header *head, struct ctl_table *table)
 {
 	int mode = table->mode;
-
-#ifdef CONFIG_CHECKPOINT_RESTORE
 	struct ipc_namespace *ns = current->nsproxy->ipc_ns;
 
+#ifdef CONFIG_CHECKPOINT_RESTORE
 	if (((table->data == &ns->ids[IPC_SEM_IDS].next_id) ||
 	     (table->data == &ns->ids[IPC_MSG_IDS].next_id) ||
 	     (table->data == &ns->ids[IPC_SHM_IDS].next_id)) &&
 	    checkpoint_restore_ns_capable(ns->user_ns))
 		mode = 0666;
+	else
 #endif
+	if (ns_capable(ns->user_ns, CAP_SYS_RESOURCE))
+		mode = 0666;
+
 	return mode;
 }
 
-- 
2.33.3