linux-kernel - [PATCH] ipc: check checkpoint_restore_ns

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Message-Id: <20210916163717.3179496-1-mclapinski@google.com>
Date:   Thu, 16 Sep 2021 18:37:17 +0200
From:   Michal Clapinski <mclapinski@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Michal Clapinski <mclapinski@...gle.com>
Subject: [PATCH] ipc: check checkpoint_restore_ns_capable() to modify C/R proc files

This commit removes the requirement to be root to modify sem_next_id,
msg_next_id and shm_next_id and checks checkpoint_restore_ns_capable
instead.

Since those files are specific to the IPC namespace, there is no reason
they should require root privileges. This is similar to ns_last_pid,
which also only checks checkpoint_restore_ns_capable.

Signed-off-by: Michal Clapinski <mclapinski@...gle.com>
---
 ipc/ipc_sysctl.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index 3f312bf2b116..f8e27203ca49 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -104,6 +104,19 @@ static int proc_ipc_sem_dointvec(struct ctl_table *table, int write,
 	return ret;
 }
 
+#ifdef CONFIG_CHECKPOINT_RESTORE
+static int proc_ipc_dointvec_minmax_checkpoint_restore(struct ctl_table *table,
+		int write, void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct user_namespace *user_ns = current->nsproxy->ipc_ns->user_ns;
+
+	if (write && !checkpoint_restore_ns_capable(user_ns))
+		return -EPERM;
+
+	return proc_ipc_dointvec_minmax(table, write, buffer, lenp, ppos);
+}
+#endif
+
 #else
 #define proc_ipc_doulongvec_minmax NULL
 #define proc_ipc_dointvec	   NULL
@@ -111,6 +124,9 @@ static int proc_ipc_sem_dointvec(struct ctl_table *table, int write,
 #define proc_ipc_dointvec_minmax_orphans   NULL
 #define proc_ipc_auto_msgmni	   NULL
 #define proc_ipc_sem_dointvec	   NULL
+#ifdef CONFIG_CHECKPOINT_RESTORE
+#define proc_ipc_dointvec_minmax_checkpoint_restore	NULL
+#endif	/* CONFIG_CHECKPOINT_RESTORE */
 #endif
 
 int ipc_mni = IPCMNI;
@@ -198,8 +214,8 @@ static struct ctl_table ipc_kern_table[] = {
 		.procname	= "sem_next_id",
 		.data		= &init_ipc_ns.ids[IPC_SEM_IDS].next_id,
 		.maxlen		= sizeof(init_ipc_ns.ids[IPC_SEM_IDS].next_id),
-		.mode		= 0644,
-		.proc_handler	= proc_ipc_dointvec_minmax,
+		.mode		= 0666,
+		.proc_handler	= proc_ipc_dointvec_minmax_checkpoint_restore,
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_INT_MAX,
 	},
@@ -207,8 +223,8 @@ static struct ctl_table ipc_kern_table[] = {
 		.procname	= "msg_next_id",
 		.data		= &init_ipc_ns.ids[IPC_MSG_IDS].next_id,
 		.maxlen		= sizeof(init_ipc_ns.ids[IPC_MSG_IDS].next_id),
-		.mode		= 0644,
-		.proc_handler	= proc_ipc_dointvec_minmax,
+		.mode		= 0666,
+		.proc_handler	= proc_ipc_dointvec_minmax_checkpoint_restore,
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_INT_MAX,
 	},
@@ -216,8 +232,8 @@ static struct ctl_table ipc_kern_table[] = {
 		.procname	= "shm_next_id",
 		.data		= &init_ipc_ns.ids[IPC_SHM_IDS].next_id,
 		.maxlen		= sizeof(init_ipc_ns.ids[IPC_SHM_IDS].next_id),
-		.mode		= 0644,
-		.proc_handler	= proc_ipc_dointvec_minmax,
+		.mode		= 0666,
+		.proc_handler	= proc_ipc_dointvec_minmax_checkpoint_restore,
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_INT_MAX,
 	},
-- 
2.33.0.309.g3052b89438-goog