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IB/ucma: Fix theoretical user triggered use-after-free

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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>
This commit is contained in:
Jason Gunthorpe 2015-08-04 17:13:32 -06:00 committed by Doug Ledford
parent b8ac311246
commit 7e967fd0b8
1 changed files with 3 additions and 3 deletions
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6
drivers/infiniband/core/ucma.c
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@ -1321,10 +1321,10 @@ static ssize_t ucma_leave_multicast(struct ucma_file *file,
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)) {