ipc: drop ipc_lock()

ipc/util.c contains multiple functions to get the ipc object pointer given
an id number.

There are two sets of function: One set verifies the sequence counter part
of the id number, other functions do not check the sequence counter.

The standard for function names in ipc/util.c is
- ..._check() functions verify the sequence counter
- ..._idr() functions do not verify the sequence counter

ipc_lock() is an exception: It does not verify the sequence counter value,
but this is not obvious from the function name.

Furthermore, shm.c is the only user of this helper.  Thus, we can simply
move the logic into shm_lock() and get rid of the function altogether.

[manfred@colorfullife.com: most of changelog]
Link: http://lkml.kernel.org/r/20180712185241.4017-7-manfred@colorfullife.com
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Kees Cook <keescook@chromium.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 36 deletions

diff --git a/ipc/util.c b/ipc/util.c
index dcb4370..bd1863b 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -589,42 +589,6 @@ struct kern_ipc_perm *ipc_obtain_object_idr(struct ipc_ids *ids, int id)
 }
 
 /**
- * ipc_lock - lock an ipc structure without rwsem held
- * @ids: ipc identifier set
- * @id: ipc id to look for
- *
- * Look for an id in the ipc ids idr and lock the associated ipc object.
- *
- * The ipc object is locked on successful exit.
- */
-struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
-{
-	struct kern_ipc_perm *out;
-
-	rcu_read_lock();
-	out = ipc_obtain_object_idr(ids, id);
-	if (IS_ERR(out))
-		goto err;
-
-	spin_lock(&out->lock);
-
-	/*
-	 * ipc_rmid() may have already freed the ID while ipc_lock()
-	 * was spinning: here verify that the structure is still valid.
-	 * Upon races with RMID, return -EIDRM, thus indicating that
-	 * the ID points to a removed identifier.
-	 */
-	if (ipc_valid_object(out))
-		return out;
-
-	spin_unlock(&out->lock);
-	out = ERR_PTR(-EIDRM);
-err:
-	rcu_read_unlock();
-	return out;
-}
-
-/**
  * ipc_obtain_object_check
  * @ids: ipc identifier set
  * @id: ipc id to look for