linux-kernel - [PATCH 14/20] ipc/shm.c: Avoid ipc_rcu_putref for failed ipc

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Date:   Thu, 25 May 2017 20:51:01 +0200
From:   Manfred Spraul <manfred@...orfullife.com>
To:     mtk.manpages@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, 1vier1@....de,
        Davidlohr Bueso <dave@...olabs.net>, mingo@...nel.org,
        peterz@...radead.org, fabf@...net.be,
        Manfred Spraul <manfred@...orfullife.com>
Subject: [PATCH 14/20] ipc/shm.c: Avoid ipc_rcu_putref for failed ipc_addid()

Loosely based on a patch from Kees Cook <keescook@...omium.org>:
- id and error can be merged
- if operations before ipc_addid() fail, then use call_rcu() directly.

The difference is that call_rcu is used for failures after
security_shm_alloc(), to continue to guaranteed an rcu delay for
security_sem_free().

Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
Cc: Kees Cook <keescook@...omium.org>
---
 ipc/shm.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/ipc/shm.c b/ipc/shm.c
index c9f1f30..cb1d97e 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -548,7 +548,6 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 	size_t numpages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	struct file *file;
 	char name[13];
-	int id;
 	vm_flags_t acctflag = 0;
 
 	if (size < SHMMIN || size > ns->shm_ctlmax)
@@ -617,11 +616,9 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 	shp->shm_file = file;
 	shp->shm_creator = current;
 
-	id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
-	if (id < 0) {
-		error = id;
+	error = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
+	if (error < 0)
 		goto no_id;
-	}
 
 	list_add(&shp->shm_clist, &current->sysvshm.shm_clist);
 
@@ -643,7 +640,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 		user_shm_unlock(size, shp->mlock_user);
 	fput(file);
 no_file:
-	ipc_rcu_putref(&shp->shm_perm, shm_rcu_free);
+	call_rcu(&shp->shm_perm.rcu, shm_rcu_free);
 	return error;
 }
 
-- 
2.9.3