[PATCH v8 2/5] ipc: IPCMNI limit check for semmni

[Waiman Long]

For SysV semaphores, the semmni value is the last part of the 4-element
sem number array. To make semmni behave in a similar way to msgmni and
shmmni, we can't directly use the _minmax handler. Instead, a special
sem specific handler is added to check the last argument to make sure
that it is limited to the [0, IPCMNI] range. An error will be returned
if this is not the case.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 ipc/ipc_sysctl.c | 23 ++++++++++++++++++++++-
 ipc/util.h       |  9 +++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index f87cb29..49f9bf4 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -88,12 +88,33 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
 	return proc_dointvec_minmax(&ipc_table, write, buffer, lenp, ppos);
 }
 
+static int proc_ipc_sem_dointvec(struct ctl_table *table, int write,
+	void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	int ret, semmni;
+	struct ipc_namespace *ns = current->nsproxy->ipc_ns;
+
+	semmni = ns->sem_ctls[3];
+	ret = proc_ipc_dointvec(table, write, buffer, lenp, ppos);
+
+	if (!ret)
+		ret = sem_check_semmni(current->nsproxy->ipc_ns);
+
+	/*
+	 * Reset the semmni value if an error happens.
+	 */
+	if (ret)
+		ns->sem_ctls[3] = semmni;
+	return ret;
+}
+
 #else
 #define proc_ipc_doulongvec_minmax NULL
 #define proc_ipc_dointvec	   NULL
 #define proc_ipc_dointvec_minmax   NULL
 #define proc_ipc_dointvec_minmax_orphans   NULL
 #define proc_ipc_auto_msgmni	   NULL
+#define proc_ipc_sem_dointvec	   NULL
 #endif
 
 static int zero;
@@ -175,7 +196,7 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
 		.data		= &init_ipc_ns.sem_ctls,
 		.maxlen		= 4*sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_ipc_dointvec,
+		.proc_handler	= proc_ipc_sem_dointvec,
 	},
 #ifdef CONFIG_CHECKPOINT_RESTORE
 	{
diff --git a/ipc/util.h b/ipc/util.h
index 0aba323..8e9c52c 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -218,6 +218,15 @@ int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
 void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
 		void (*free)(struct ipc_namespace *, struct kern_ipc_perm *));
 
+static inline int sem_check_semmni(struct ipc_namespace *ns) {
+	/*
+	 * Check semmni range [0, IPCMNI]
+	 * semmni is the last element of sem_ctls[4] array
+	 */
+	return ((ns->sem_ctls[3] < 0) || (ns->sem_ctls[3] > IPCMNI))
+		? -ERANGE : 0;
+}
+
 #ifdef CONFIG_COMPAT
 #include <linux/compat.h>
 struct compat_ipc_perm {
-- 
1.8.3.1