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Subject[PATCH 1/2] mm/hmm: hmm_range_fault() NULL pointer bug
Date
Although hmm_range_fault() calls find_vma() to make sure that a vma exists
before calling walk_page_range(), hmm_vma_walk_hole() can still be called
with walk->vma == NULL if the start and end address are not contained
within the vma range.

hmm_range_fault() /* calls find_vma() but no range check */
walk_page_range() /* calls find_vma(), sets walk->vma = NULL */
__walk_page_range()
walk_pgd_range()
walk_p4d_range()
walk_pud_range()
hmm_vma_walk_hole()
hmm_vma_walk_hole_()
hmm_vma_do_fault()
handle_mm_fault(vma=0)

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
---
mm/hmm.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index fc05c8fe78b4..29371485fe94 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -229,6 +229,9 @@ static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
struct vm_area_struct *vma = walk->vma;
vm_fault_t ret;

+ if (!vma)
+ goto err;
+
if (hmm_vma_walk->flags & HMM_FAULT_ALLOW_RETRY)
flags |= FAULT_FLAG_ALLOW_RETRY;
if (write_fault)
@@ -239,12 +242,14 @@ static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
/* Note, handle_mm_fault did up_read(&mm->mmap_sem)) */
return -EAGAIN;
}
- if (ret & VM_FAULT_ERROR) {
- *pfn = range->values[HMM_PFN_ERROR];
- return -EFAULT;
- }
+ if (ret & VM_FAULT_ERROR)
+ goto err;

return -EBUSY;
+
+err:
+ *pfn = range->values[HMM_PFN_ERROR];
+ return -EFAULT;
}

static int hmm_pfns_bad(unsigned long addr,
--
2.20.1
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