Commit f8b59184 authored Jun 30, 2015 by Davidlohr Bueso Committed by Linus Torvalds Jun 30, 2015

ipc,sysv: make return -EIDRM when racing with RMID consistent



The ipc_lock helper is used by all forms of sysv ipc to acquire the ipc
object's spinlock.  Upon error (bogus identifier), we always return
-EINVAL, whether the problem be in the idr path or because we raced with a
task performing RMID.  For the later, however, all ipc related manpages,
state the that for:

       EIDRM  <ID> points to a removed identifier.

And return:

       EINVAL Invalid <ID> value, or unaligned, etc.

Which (EINVAL) should only return once the ipc resource is deleted.  For
all types of ipc this is done immediately upon a RMID command.  However,
shared memory behaves slightly different as it can merely mark a segment
for deletion, and delay the actual freeing until there are no more active
consumers.  Per shmctl(IPC_RMID) manpage:

""
Mark  the  segment to be destroyed.  The segment will only actually
be destroyed after the last process detaches it (i.e., when the
shm_nattch member of the associated structure shmid_ds is zero).
""

Unlike ipc_lock, paths that behave "correctly", at least per the manpage,
involve controlling the ipc resource via *ctl(), doing the exact same
validity check as ipc_lock after right acquiring the spinlock:

	if (!ipc_valid_object()) {
		err = -EIDRM;
		goto out_unlock;
	}

Thus make ipc_lock consistent with the rest of ipc code and return -EIDRM
in ipc_lock when !ipc_valid_object().

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 55b7ae50

ipc/util.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -583,19 +583,22 @@ struct kern_ipc_perm ipc_lock(struct ipc_ids ids, int id)
		rcu_read_lock();
		out = ipc_obtain_object_idr(ids, id);
		if (IS_ERR(out))
		goto err1;
		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
		/*
		* 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(-EINVAL);
		err1:
		out = ERR_PTR(-EIDRM);
		err:
		rcu_read_unlock();
		return out;
		}

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