IB/ucma: Fix theoretical user triggered use-after-free
Something like this:
CPU A CPU B
Acked-by: Sean Hefty <sean.hefty@intel.com>
======================== ================================
ucma_destroy_id()
wait_for_completion()
.. anything
ucma_put_ctx()
complete()
.. continues ...
ucma_leave_multicast()
mutex_lock(mut)
atomic_inc(ctx->ref)
mutex_unlock(mut)
ucma_free_ctx()
ucma_cleanup_multicast()
mutex_lock(mut)
kfree(mc)
rdma_leave_multicast(mc->ctx->cm_id,..
Fix it by latching the ref at 0. Once it goes to 0 mc and ctx cannot
leave the mutex(mut) protection.
The other atomic_inc in ucma_get_ctx is OK because mutex(mut) protects
it from racing with ucma_destroy_id.
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Acked-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
index 29b2121..acac9ea 100644
--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -1321,10 +1321,10 @@
mc = ERR_PTR(-ENOENT);
else if (mc->ctx->file != file)
mc = ERR_PTR(-EINVAL);
- else {
+ else if (!atomic_inc_not_zero(&mc->ctx->ref))
+ mc = ERR_PTR(-ENXIO);
+ else
idr_remove(&multicast_idr, mc->id);
- atomic_inc(&mc->ctx->ref);
- }
mutex_unlock(&mut);
if (IS_ERR(mc)) {