vmalloc: fix buffer overflow in vrealloc_node_align()

CVE-2026-46281

What is CVE-2026-46281?

In the Linux kernel, the following vulnerability has been resolved:

vmalloc: fix buffer overflow in vrealloc_node_align()

Commit 4c5d3365882d ("mm/vmalloc: allow to set node and align in vrealloc") added the ability to force a new allocation if the current pointer is on the wrong NUMA node, or if an alignment constraint is not met, even if the user is shrinking the allocation.

On this path (need_realloc), the code allocates a new object of 'size' bytes and then memcpy()s 'old_size' bytes into it. If the request is to shrink the object (size < old_size), this results in an out-of-bounds write on the new buffer.

Fix this by bounding the copy length by the new allocation size.

References