We can divide vma_adjust() into two categories based on whether the *insert* is NULL or not. And when *insert* is NULL, it has two users: mremap() and shift_arg_pages(). For the second vma_adjust() in shift_arg_pages(), the vma must not have next. Otherwise vma_adjust() would expand next->vm_start instead of just shift the vma. Fortunately, shift_arg_pages() is only used in setup_arg_pages() to move stack, which is placed on the top of the address range. This means the vma is not expected to have a next. Since mremap() calls vma_adjust() to expand itself, shift_arg_pages() is the only case it may fall into mprotect case 4 by accident. Let's add a BUG_ON() and comment to inform the following audience. Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> --- fs/exec.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/exec.c b/fs/exec.c index a91003e28eaa..3ff44ab0d112 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -682,6 +682,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift) struct mmu_gather tlb; BUG_ON(new_start > new_end); + BUG_ON(vma->vm_next); /* * ensure there are no vmas between where we want to go @@ -726,6 +727,8 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift) /* * Shrink the vma to just the new range. Always succeeds. + * Since !vma->vm_next, __vma_adjust() would not go to mprotect case + * 4 to expand next. */ vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL); -- 2.20.1 (Apple Git-117)
