Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Sender: vjitta=codeaurora.org@mg.codeaurora.org
DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 996FCC433CA
From:   vjitta@codeaurora.org
To:     akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Cc:     vjitta@codeaurora.org, vinmenon@codeaurora.org
Subject: [PATCH] mm: vmalloc: Prevent use after free in _vm_unmap_aliases
Date:   Thu, 18 Mar 2021 15:38:25 +0530
Message-Id: <1616062105-23263-1-git-send-email-vjitta@codeaurora.org>
Precedence: bulk

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