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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ddc17ba55bsm13079025ad.57.2026.09.19.14.36.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 14:36:53 -0700 (PDT) From: Hui Peng To: gregkh@linuxfoundation.org, arve@android.com, tkjos@android.com, brauner@kernel.org, cmllamas@google.com, aliceryhl@google.com Cc: linux-kernel@vger.kernel.org Subject: [PATCH] binder: forbid VMA splitting and mremap on binder mmap Date: Sat, 19 Sep 2026 21:36:53 +0000 Message-ID: <20260919213653.3317260-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit `binder_vm_ops` does not implement `.may_split` or `.mremap`, and `binder_vma_close()` unconditionally calls `binder_alloc_vma_close(&proc->alloc)` (which sets `alloc->vma = NULL`). If userspace calls `munmap()` on a sub-range of the binder mapping (or `mremap()` to move/split a sub-range), the VMA is split into two VMAs sharing the same `binder_proc`, and `binder_vma_close()` runs on the unmapped half and clears `alloc->vma = NULL` while the remaining VMA stays mapped in the process's address space, desynchronizing `alloc->vma` from the remaining VMA. Implement `.may_split` and `.mremap` returning `-EINVAL` in `binder_vm_ops` and check `vma->vm_start == proc->alloc.vm_start` in `binder_vma_close()`. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Assisted-by: LLM Signed-off-by: Hui Peng --- drivers/android/binder.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 8f2ef1bd539f..1c7218e599a1 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -6023,9 +6058,21 @@ static void binder_vma_close(struct vm_area_struct *vma) proc->pid, vma->vm_start, vma->vm_end, (vma->vm_end - vma->vm_start) / SZ_1K, vma->vm_flags, (unsigned long)pgprot_val(vma->vm_page_prot)); + if (vma->vm_start != proc->alloc.vm_start) + return; binder_alloc_vma_close(&proc->alloc); } +static int binder_may_split(struct vm_area_struct *vma, unsigned long addr) +{ + return -EINVAL; +} + +static int binder_mremap(struct vm_area_struct *vma) +{ + return -EINVAL; +} + VISIBLE_IF_KUNIT vm_fault_t binder_vm_fault(struct vm_fault *vmf) { return VM_FAULT_SIGBUS; @@ -6035,6 +6082,8 @@ EXPORT_SYMBOL_IF_KUNIT(binder_vm_fault); static const struct vm_operations_struct binder_vm_ops = { .open = binder_vma_open, .close = binder_vma_close, + .may_split = binder_may_split, + .mremap = binder_mremap, .fault = binder_vm_fault, };