[Xen-changelog] [xen stable-4.12] xmalloc: guard against integer overflow

[patchbot@xxxxxxx]

commit b165d136b457ebb8c1486d83b7ee96504849e95a
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Mar 5 11:20:12 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 5 11:20:12 2020 +0100

    xmalloc: guard against integer overflow
    
    There are hypercall handling paths (EFI ones are what this was found
    with) needing to allocate buffers of a caller specified size. This is
    generally fine, as our page allocator enforces an upper bound on all
    allocations. However, certain extremely large sizes could, when adding
    in allocator overhead, result in an apparently tiny allocation size,
    which would typically result in either a successful allocation, but a
    severe buffer overrun when using that memory block, or in a crash right
    in the allocator code.
    
    Reported-by: Ilja Van Sprundel <ivansprundel@xxxxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>
    master commit: cf38b4926e2b55d1d7715cff5095a7444f5ed42d
    master date: 2020-02-06 09:53:12 +0100
---
 xen/common/xmalloc_tlsf.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/xen/common/xmalloc_tlsf.c b/xen/common/xmalloc_tlsf.c
index b256dc56cf..987e377cbb 100644
--- a/xen/common/xmalloc_tlsf.c
+++ b/xen/common/xmalloc_tlsf.c
@@ -388,7 +388,17 @@ void *xmem_pool_alloc(unsigned long size, struct xmem_pool 
*pool)
         pool->init_region = region;
     }
 
-    size = (size < MIN_BLOCK_SIZE) ? MIN_BLOCK_SIZE : ROUNDUP_SIZE(size);
+    if ( size < MIN_BLOCK_SIZE )
+        size = MIN_BLOCK_SIZE;
+    else
+    {
+        tmp_size = ROUNDUP_SIZE(size);
+        /* Guard against overflow. */
+        if ( tmp_size < size )
+            return NULL;
+        size = tmp_size;
+    }
+
     /* Rounding up the requested size and calculating fl and sl */
 
     spin_lock(&pool->lock);
@@ -583,6 +593,10 @@ void *_xmalloc(unsigned long size, unsigned long align)
         align = MEM_ALIGN;
     size += align - MEM_ALIGN;
 
+    /* Guard against overflow. */
+    if ( size < align - MEM_ALIGN )
+        return NULL;
+
     if ( !xenpool )
         tlsf_init();
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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