From 309d08d9b3a3659ab3f239d27d4e38b670b08fc9 Mon Sep 17 00:00:00 2001 From: Liu Zixian Date: Sat, 5 Dec 2020 22:15:15 -0800 Subject: mm/mmap.c: fix mmap return value when vma is merged after call_mmap() On success, mmap should return the begin address of newly mapped area, but patch "mm: mmap: merge vma after call_mmap() if possible" set vm_start of newly merged vma to return value addr. Users of mmap will get wrong address if vma is merged after call_mmap(). We fix this by moving the assignment to addr before merging vma. We have a driver which changes vm_flags, and this bug is found by our testcases. Fixes: d70cec898324 ("mm: mmap: merge vma after call_mmap() if possible") Signed-off-by: Liu Zixian Signed-off-by: Andrew Morton Reviewed-by: Jason Gunthorpe Reviewed-by: David Hildenbrand Cc: Miaohe Lin Cc: Hongxiang Lou Cc: Hu Shiyuan Cc: Matthew Wilcox Link: https://lkml.kernel.org/r/20201203085350.22624-1-liuzixian4@huawei.com Signed-off-by: Linus Torvalds --- mm/mmap.c | 26 ++++++++++++-------------- 1 file changed, 12 insertions(+), 14 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index d91ecb00d38c..5c8b4485860d 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1808,6 +1808,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr, if (error) goto unmap_and_free_vma; + /* Can addr have changed?? + * + * Answer: Yes, several device drivers can do it in their + * f_op->mmap method. -DaveM + * Bug: If addr is changed, prev, rb_link, rb_parent should + * be updated for vma_link() + */ + WARN_ON_ONCE(addr != vma->vm_start); + + addr = vma->vm_start; + /* If vm_flags changed after call_mmap(), we should try merge vma again * as we may succeed this time. */ @@ -1822,25 +1833,12 @@ unsigned long mmap_region(struct file *file, unsigned long addr, fput(vma->vm_file); vm_area_free(vma); vma = merge; - /* Update vm_flags and possible addr to pick up the change. We don't - * warn here if addr changed as the vma is not linked by vma_link(). - */ - addr = vma->vm_start; + /* Update vm_flags to pick up the change. */ vm_flags = vma->vm_flags; goto unmap_writable; } } - /* Can addr have changed?? - * - * Answer: Yes, several device drivers can do it in their - * f_op->mmap method. -DaveM - * Bug: If addr is changed, prev, rb_link, rb_parent should - * be updated for vma_link() - */ - WARN_ON_ONCE(addr != vma->vm_start); - - addr = vma->vm_start; vm_flags = vma->vm_flags; } else if (vm_flags & VM_SHARED) { error = shmem_zero_setup(vma); -- cgit v1.2.3