From: Vijayanand Jitta vjitta@codeaurora.org

mainline inclusion from mainline-5.13-rc1 commit ad216c0316ad6391d90f4de0a7f59396b2925a06 category: feature bugzilla: NA CVE: NA

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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@codeauror... Signed-off-by: Vijayanand Jitta vjitta@codeaurora.org Reviewed-by: Uladzislau Rezki (Sony) urezki@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Rui Xiang rui.xiang@huawei.com Reviewed-by: Ding Tianhong dingtianhong@huawei.com Reviewed-by: Weilong Chen chenweilong@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- mm/vmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 8c70131e0b078..011a84ebec04d 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1953,7 +1953,7 @@ void vm_unmap_aliases(void) 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;