linux-kernel - [PATCH 3.16 063/366] ipc,shm: move BUG_ON check into shm

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Message-ID: <lsq.1539530741.89845255@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Davidlohr Bueso" <dbueso@...e.de>,
        "Manfred Spraul" <manfred@...orfullife.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Davidlohr Bueso" <dave@...olabs.net>
Subject: [PATCH 3.16 063/366] ipc,shm: move BUG_ON check into shm_lock

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Davidlohr Bueso <dave@...olabs.net>

commit c5c8975b2eb4eb7604e8ce4f762987f56d2a96a2 upstream.

Upon every shm_lock call, we BUG_ON if an error was returned, indicating
racing either in idr or in shm_destroy.  Move this logic into the locking.

[akpm@...ux-foundation.org: simplify code]
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
Cc: Manfred Spraul <manfred@...orfullife.com>
Cc: Davidlohr Bueso <dave@...olabs.net>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 ipc/shm.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -155,8 +155,11 @@ static inline struct shmid_kernel *shm_l
 {
 	struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);
 
-	if (IS_ERR(ipcp))
-		return (struct shmid_kernel *)ipcp;
+	/*
+	 * We raced in the idr lookup or with shm_destroy().  Either way, the
+	 * ID is busted.
+	 */
+	BUG_ON(IS_ERR(ipcp));
 
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
@@ -190,7 +193,6 @@ static void shm_open(struct vm_area_stru
 	struct shmid_kernel *shp;
 
 	shp = shm_lock(sfd->ns, sfd->id);
-	BUG_ON(IS_ERR(shp));
 	shp->shm_atim = get_seconds();
 	shp->shm_lprid = task_tgid_vnr(current);
 	shp->shm_nattch++;
@@ -256,7 +258,6 @@ static void shm_close(struct vm_area_str
 	down_write(&shm_ids(ns).rwsem);
 	/* remove from the list of attaches of the shm segment */
 	shp = shm_lock(ns, sfd->id);
-	BUG_ON(IS_ERR(shp));
 	shp->shm_lprid = task_tgid_vnr(current);
 	shp->shm_dtim = get_seconds();
 	shp->shm_nattch--;
@@ -1199,7 +1200,6 @@ out_fput:
 out_nattch:
 	down_write(&shm_ids(ns).rwsem);
 	shp = shm_lock(ns, shmid);
-	BUG_ON(IS_ERR(shp));
 	shp->shm_nattch--;
 	if (shm_may_destroy(ns, shp))
 		shm_destroy(ns, shp);