From: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx> Subject: mm: vmalloc: prevent use after free in _vm_unmap_aliases 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. Link: https://lkml.kernel.org/r/1616062105-23263-1-git-send-email-vjitta@xxxxxxxxxxxxxx Signed-off-by: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx> Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/vmalloc.c~mm-vmalloc-prevent-use-after-free-in-_vm_unmap_aliases +++ a/mm/vmalloc.c @@ -2040,7 +2040,7 @@ static void _vm_unmap_aliases(unsigned l 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; _
