Messages in this thread Patch in this message | | | From | vjitta@codeauro ... | Subject | [PATCH] mm: vmalloc: Prevent use after free in _vm_unmap_aliases | Date | Thu, 18 Mar 2021 15:38:25 +0530 |
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From: Vijayanand Jitta <vjitta@codeaurora.org>
A potential use after free can occur in _vm_unmap_aliases where an already freed vmap_area could be accessed, Consider the following scenario:
Process 1 Process 2
__vm_unmap_aliases __vm_unmap_aliases purge_fragmented_blocks_allcpus rcu_read_lock() rcu_read_lock() list_del_rcu(&vb->free_list) list_for_each_entry_rcu(vb .. ) __purge_vmap_area_lazy kmem_cache_free(va) va_start = vb->va->va_start
Here Process 1 is in purge path and it does list_del_rcu on vmap_block and later frees the vmap_area, since Process 2 was holding the rcu lock at this time vmap_block will still be present in and Process 2 accesse it and thereby it tries to access vmap_area of that vmap_block which was already freed by Process 1 and this results in use after free.
Fix this by adding a check for vb->dirty before accessing vmap_area structure since vb->dirty will be set to VMAP_BBMAP_BITS in purge path checking for this will prevent the use after free.
Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org> --- mm/vmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index d5f2a84..ebb6f57 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1762,7 +1762,7 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush) rcu_read_lock(); list_for_each_entry_rcu(vb, &vbq->free, free_list) { spin_lock(&vb->lock); - if (vb->dirty) { + if (vb->dirty && vb->dirty != VMAP_BBMAP_BITS) { unsigned long va_start = vb->va->va_start; unsigned long s, e; -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation 2.7.4
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