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Groups > linux.kernel > #1650745

[PATCH 09/20] ipc/sem: Avoid ipc_rcu_alloc()

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From: Kees Cook <keescook@chromium.org>

Instead of using ipc_rcu_alloc() which only performs the refcount
bump, open code it to perform better sem-specific checks. This
also allows for sem_array structure layout to be randomized in the
future.

Signed-off-by: Kees Cook <keescook@chromium.org>

[manfred@colorfullife.com: Rediff, because the memset was
temporarily inside ipc_rcu_alloc()]

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
---
 ipc/sem.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index a04c4d6..445a5b5 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -451,6 +451,25 @@ static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
 	ipc_rmid(&sem_ids(ns), &s->sem_perm);
 }
 
+static struct sem_array *sem_alloc(size_t nsems)
+{
+	struct sem_array *sma;
+	size_t size;
+
+	if (nsems > (INT_MAX - sizeof(*sma)) / sizeof(sma->sems[0]))
+		return NULL;
+
+	size = sizeof(*sma) + nsems * sizeof(sma->sems[0]);
+	sma = kvmalloc(size, GFP_KERNEL);
+	if (unlikely(!sma))
+		return NULL;
+
+	memset(sma, 0, size);
+	atomic_set(&sma->sem_perm.refcount, 1);
+
+	return sma;
+}
+
 /**
  * newary - Create a new semaphore set
  * @ns: namespace
@@ -463,7 +482,6 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 	int id;
 	int retval;
 	struct sem_array *sma;
-	int size;
 	key_t key = params->key;
 	int nsems = params->u.nsems;
 	int semflg = params->flg;
@@ -474,10 +492,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 	if (ns->used_sems + nsems > ns->sc_semmns)
 		return -ENOSPC;
 
-	BUILD_BUG_ON(offsetof(struct sem_array, sem_perm) != 0);
-
-	size = sizeof(*sma) + nsems * sizeof(sma->sems[0]);
-	sma = container_of(ipc_rcu_alloc(size), struct sem_array, sem_perm);
+	sma = sem_alloc(nsems);
 	if (!sma)
 		return -ENOMEM;
 
-- 
2.9.3

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[PATCH 0/20 V3] Misc cleanups for ipc Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 05/20] ipc/sem: Do not use ipc_rcu_free() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 08/20] ipc/util: Drop ipc_rcu_free() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 15/20] ipc/msg.c: Avoid ipc_rcu_putref for failed ipc_addid() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 19/20] ipc/sem: Drop __sem_free() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 20/20] ipc/util.h: Update documentation for ipc_getref() and ipc_putref() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 09/20] ipc/sem: Avoid ipc_rcu_alloc() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 17/20] ipc/shm: Remove special shm_alloc/free Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 11/20] ipc/msg: Avoid ipc_rcu_alloc() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 12/20] ipc/util: Drop ipc_rcu_alloc() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 16/20] ipc: Move atomic_set() to where it is needed Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 04/20] ipc: Drop non-RCU allocation Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
    Re: [PATCH 04/20] ipc: Drop non-RCU allocation Kees Cook <keescook@chromium.org> - 2017-05-25 21:40 +0200
  [PATCH 03/20] include/linux/sem.h: Correctly document sem_ctime Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 07/20] ipc/msg: Do not use ipc_rcu_free() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  [PATCH 10/20] ipc/shm: Avoid ipc_rcu_alloc() Manfred Spraul <manfred@colorfullife.com> - 2017-05-25 21:00 +0200
  Re: [PATCH 0/20 V3] Misc cleanups for ipc Kees Cook <keescook@chromium.org> - 2017-05-25 21:50 +0200
    Re: [PATCH 0/20 V3] Misc cleanups for ipc Manfred Spraul <manfred@colorfullife.com> - 2017-05-26 04:00 +0200

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