The ashmem driver did not check that the size/offset of the vma passed to its .mmap() function was not larger than the ashmem object being mapped. This could cause mmap() to succeed, even though accessing parts of the mapping would later fail with a segmentation fault.
Ensure an error is returned by the ashmem_mmap() function if the vma size is larger than the ashmem object size. This enables safer handling of the problem in userspace. Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> Cc: Arve Hjønnevåg <a...@android.com> Cc: Todd Kjos <tk...@android.com> Cc: Martijn Coenen <m...@android.com> Cc: de...@driverdev.osuosl.org Cc: linux-kernel@vger.kernel.org Cc: kernel-t...@android.com Cc: Joel Fernandes <j...@joelfernandes.org> Signed-off-by: Alistair Strachan <astrac...@google.com> --- v2: Removed unnecessary use of unlikely() macro drivers/staging/android/ashmem.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index c6386e4f5c9b..e392358ec244 100644 --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -366,6 +366,12 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) goto out; } + /* requested mapping size larger than object size */ + if (vma->vm_end - vma->vm_start > PAGE_ALIGN(asma->size)) { + ret = -EINVAL; + goto out; + } + /* requested protection bits must match our allowed protection mask */ if ((vma->vm_flags & ~calc_vm_prot_bits(asma->prot_mask, 0)) & calc_vm_prot_bits(PROT_MASK, 0)) {