[PATCH] mm/hmm/test: use after free in dmirror_allocate_chunk()

[Dan Carpenter]

The error handling code does this:

err_free:
        kfree(devmem);
        ^^^^^^^^^^^^^
err_release:
        release_mem_region(devmem->pagemap.range.start, 
range_len(&devmem->pagemap.range));
                           ^^^^^^^^
The problem is that when we use "devmem->pagemap.range.start" the
"devmem" pointer is either NULL or freed.

Neither the allocation nor the call to request_free_mem_region() has to
be done under the lock so I moved those to the start of the function.

Fixes: b2ef9f5a5cb3 ("mm/hmm/test: add selftest driver for HMM")
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
---
It's weird that I didn't catch the use after free when this code was
merged in May...  My bad.  Not sure what happened there.  How I found
this was that I have been reviewing release_mem_region() leaks and the
NULL dereference path is a leak.


 lib/test_hmm.c | 47 ++++++++++++++++++++++++-----------------------
 1 file changed, 24 insertions(+), 23 deletions(-)

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index c8133f50160b..0503c78cb322 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -459,6 +459,22 @@ static bool dmirror_allocate_chunk(struct dmirror_device 
*mdevice,
        unsigned long pfn_last;
        void *ptr;
 
+       devmem = kzalloc(sizeof(*devmem), GFP_KERNEL);
+       if (!devmem)
+               return -ENOMEM;
+
+       res = request_free_mem_region(&iomem_resource, DEVMEM_CHUNK_SIZE,
+                                     "hmm_dmirror");
+       if (IS_ERR(res))
+               goto err_devmem;
+
+       devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
+       devmem->pagemap.range.start = res->start;
+       devmem->pagemap.range.end = res->end;
+       devmem->pagemap.nr_range = 1;
+       devmem->pagemap.ops = &dmirror_devmem_ops;
+       devmem->pagemap.owner = mdevice;
+
        mutex_lock(&mdevice->devmem_lock);
 
        if (mdevice->devmem_count == mdevice->devmem_capacity) {
@@ -471,30 +487,16 @@ static bool dmirror_allocate_chunk(struct dmirror_device 
*mdevice,
                                sizeof(new_chunks[0]) * new_capacity,
                                GFP_KERNEL);
                if (!new_chunks)
-                       goto err;
+                       goto err_release;
                mdevice->devmem_capacity = new_capacity;
                mdevice->devmem_chunks = new_chunks;
        }
 
-       res = request_free_mem_region(&iomem_resource, DEVMEM_CHUNK_SIZE,
-                                       "hmm_dmirror");
-       if (IS_ERR(res))
-               goto err;
-
-       devmem = kzalloc(sizeof(*devmem), GFP_KERNEL);
-       if (!devmem)
-               goto err_release;
-
-       devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
-       devmem->pagemap.range.start = res->start;
-       devmem->pagemap.range.end = res->end;
-       devmem->pagemap.nr_range = 1;
-       devmem->pagemap.ops = &dmirror_devmem_ops;
-       devmem->pagemap.owner = mdevice;
-
        ptr = memremap_pages(&devmem->pagemap, numa_node_id());
-       if (IS_ERR(ptr))
-               goto err_free;
+       if (IS_ERR(ptr)) {
+               mutex_unlock(&mdevice->devmem_lock);
+               goto err_release;
+       }
 
        devmem->mdevice = mdevice;
        pfn_first = devmem->pagemap.range.start >> PAGE_SHIFT;
@@ -525,12 +527,11 @@ static bool dmirror_allocate_chunk(struct dmirror_device 
*mdevice,
 
        return true;
 
-err_free:
-       kfree(devmem);
 err_release:
        release_mem_region(devmem->pagemap.range.start, 
range_len(&devmem->pagemap.range));
-err:
-       mutex_unlock(&mdevice->devmem_lock);
+err_devmem:
+       kfree(devmem);
+
        return false;
 }
 
-- 
2.28.0