Double Free in Linux kernel RDMA/irdma rereg_user_mr
CVE-2026-43120 is a Linux kernel vulnerability in the RDMA/irdma subsystem involving memory-region re-registration via rereg_user_mr. When IB_MR_REREG_TRANS is set, the reregistration path releases the existing umem and allocates a new one in irdma_rereg_mr_trans. If a later step in irdma_rereg_mr_trans fails after the new umem has been allocated, the function releases that new umem but leaves iwmr->region non-NULL. The failure is then returned to user space, and a subsequent normal cleanup call such as ibv_dereg_mr can enter the deregistration path, observe the stale non-NULL region pointer, and invoke ib_umem_release a second time on the same object. This results in a double free condition. The fix sets iwmr->region to NULL immediately after ib_umem_release in the failure path. The vulnerable functionality was introduced by commit 5ac388db27c4 ("RDMA/irdma: Add support to re-register a memory region").
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