Add more sanity checks to the VMA that do_brk_flags() will expand.
Ensure the VMA matches basic merge requirements within the function
before calling can_vma_merge_after().
Drop the duplicate checks from vm_brk_flags() since they will be
enforced later.
Fixes: 2e7ce7d354f2 ("mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()")
Suggested-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
mm/mmap.c | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index a5eb2f175da0..5d48170fc2b2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2946,9 +2946,9 @@ static int do_brk_flags(struct ma_state *mas, struct vm_area_struct *vma,
* Expand the existing vma if possible; Note that singular lists do not
* occur after forking, so the expand will only happen on new VMAs.
*/
- if (vma &&
- (!vma->anon_vma || list_is_singular(&vma->anon_vma_chain)) &&
- ((vma->vm_flags & ~VM_SOFTDIRTY) == flags)) {
+ if (vma && vma->vm_end == addr && !vma_policy(vma) &&
+ can_vma_merge_after(vma, flags, NULL, NULL,
+ addr >> PAGE_SHIFT, NULL_VM_UFFD_CTX, NULL)) {
mas_set_range(mas, vma->vm_start, addr + len - 1);
if (mas_preallocate(mas, vma, GFP_KERNEL))
return -ENOMEM;
@@ -3035,11 +3035,6 @@ int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
goto munmap_failed;
vma = mas_prev(&mas, 0);
- if (!vma || vma->vm_end != addr || vma_policy(vma) ||
- !can_vma_merge_after(vma, flags, NULL, NULL,
- addr >> PAGE_SHIFT, NULL_VM_UFFD_CTX, NULL))
- vma = NULL;
-
ret = do_brk_flags(&mas, vma, addr, len, flags);
populate = ((mm->def_flags & VM_LOCKED) != 0);
mmap_write_unlock(mm);
--
2.35.1
