From: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> commit f4e9e0e69468583c2c6d9d5c7bfc975e292bf188 upstream. set_mempolicy_home_node() iterates over a list of VMAs and calls mbind_range() on each VMA, which also iterates over the singular list of the VMA passed in and potentially splits the VMA. Since the VMA iterator is not passed through, set_mempolicy_home_node() may now point to a stale node in the VMA tree. This can result in a UAF as reported by syzbot. Avoid the stale maple tree node by passing the VMA iterator through to the underlying call to split_vma(). mbind_range() is also overly complicated, since there are two calling functions and one already handles iterating over the VMAs. Simplify mbind_range() to only handle merging and splitting of the VMAs. Align the new loop in do_mbind() and existing loop in set_mempolicy_home_node() to use the reduced mbind_range() function. This allows for a single location of the range calculation and avoids constantly looking up the previous VMA (since this is a loop over the VMAs). Link: https://lore.kernel.org/linux-mm/000000000000c93feb05f87e24ad@xxxxxxxxxx/ Fixes: 66850be55e8e ("mm/mempolicy: use vma iterator & maple state instead of vma linked list") Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> Reported-by: syzbot+a7c1ec5b1d71ceaa5186@xxxxxxxxxxxxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20230410152205.2294819-1-Liam.Howlett@xxxxxxxxxx Tested-by: syzbot+a7c1ec5b1d71ceaa5186@xxxxxxxxxxxxxxxxxxxxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/mempolicy.c | 113 ++++++++++++++++++++++++++------------------------------- 1 file changed, 52 insertions(+), 61 deletions(-) --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -784,70 +784,56 @@ static int vma_replace_policy(struct vm_ return err; } -/* Step 2: apply policy to a range and do splits. */ -static int mbind_range(struct mm_struct *mm, unsigned long start, - unsigned long end, struct mempolicy *new_pol) +/* Split or merge the VMA (if required) and apply the new policy */ +static int mbind_range(struct vma_iterator *vmi, struct vm_area_struct *vma, + struct vm_area_struct **prev, unsigned long start, + unsigned long end, struct mempolicy *new_pol) { - MA_STATE(mas, &mm->mm_mt, start, start); - struct vm_area_struct *prev; - struct vm_area_struct *vma; - int err = 0; + struct vm_area_struct *merged; + unsigned long vmstart, vmend; pgoff_t pgoff; + int err; - prev = mas_prev(&mas, 0); - if (unlikely(!prev)) - mas_set(&mas, start); + vmend = min(end, vma->vm_end); + if (start > vma->vm_start) { + *prev = vma; + vmstart = start; + } else { + vmstart = vma->vm_start; + } - vma = mas_find(&mas, end - 1); - if (WARN_ON(!vma)) + if (mpol_equal(vma_policy(vma), new_pol)) return 0; - if (start > vma->vm_start) - prev = vma; + pgoff = vma->vm_pgoff + ((vmstart - vma->vm_start) >> PAGE_SHIFT); + merged = vma_merge(vma->vm_mm, *prev, vmstart, vmend, vma->vm_flags, + vma->anon_vma, vma->vm_file, pgoff, new_pol, + vma->vm_userfaultfd_ctx, anon_vma_name(vma)); + if (merged) { + *prev = merged; + /* vma_merge() invalidated the mas */ + mas_pause(&vmi->mas); + return vma_replace_policy(merged, new_pol); + } - for (; vma; vma = mas_next(&mas, end - 1)) { - unsigned long vmstart = max(start, vma->vm_start); - unsigned long vmend = min(end, vma->vm_end); - - if (mpol_equal(vma_policy(vma), new_pol)) - goto next; - - pgoff = vma->vm_pgoff + - ((vmstart - vma->vm_start) >> PAGE_SHIFT); - prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags, - vma->anon_vma, vma->vm_file, pgoff, - new_pol, vma->vm_userfaultfd_ctx, - anon_vma_name(vma)); - if (prev) { - /* vma_merge() invalidated the mas */ - mas_pause(&mas); - vma = prev; - goto replace; - } - if (vma->vm_start != vmstart) { - err = split_vma(vma->vm_mm, vma, vmstart, 1); - if (err) - goto out; - /* split_vma() invalidated the mas */ - mas_pause(&mas); - } - if (vma->vm_end != vmend) { - err = split_vma(vma->vm_mm, vma, vmend, 0); - if (err) - goto out; - /* split_vma() invalidated the mas */ - mas_pause(&mas); - } -replace: - err = vma_replace_policy(vma, new_pol); + if (vma->vm_start != vmstart) { + err = split_vma(vma->vm_mm, vma, vmstart, 1); if (err) - goto out; -next: - prev = vma; + return err; + /* split_vma() invalidated the mas */ + mas_pause(&vmi->mas); } -out: - return err; + if (vma->vm_end != vmend) { + err = split_vma(vma->vm_mm, vma, vmend, 0); + if (err) + return err; + /* split_vma() invalidated the mas */ + mas_pause(&vmi->mas); + } + + *prev = vma; + return vma_replace_policy(vma, new_pol); } /* Set the process memory policy */ @@ -1259,6 +1245,8 @@ static long do_mbind(unsigned long start nodemask_t *nmask, unsigned long flags) { struct mm_struct *mm = current->mm; + struct vm_area_struct *vma, *prev; + struct vma_iterator vmi; struct mempolicy *new; unsigned long end; int err; @@ -1328,7 +1316,13 @@ static long do_mbind(unsigned long start goto up_out; } - err = mbind_range(mm, start, end, new); + vma_iter_init(&vmi, mm, start); + prev = vma_prev(&vmi); + for_each_vma_range(vmi, vma, end) { + err = mbind_range(&vmi, vma, &prev, start, end, new); + if (err) + break; + } if (!err) { int nr_failed = 0; @@ -1489,10 +1483,8 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, home_node, unsigned long, flags) { struct mm_struct *mm = current->mm; - struct vm_area_struct *vma; + struct vm_area_struct *vma, *prev; struct mempolicy *new; - unsigned long vmstart; - unsigned long vmend; unsigned long end; int err = -ENOENT; VMA_ITERATOR(vmi, mm, start); @@ -1521,9 +1513,8 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, if (end == start) return 0; mmap_write_lock(mm); + prev = vma_prev(&vmi); for_each_vma_range(vmi, vma, end) { - vmstart = max(start, vma->vm_start); - vmend = min(end, vma->vm_end); new = mpol_dup(vma_policy(vma)); if (IS_ERR(new)) { err = PTR_ERR(new); @@ -1547,7 +1538,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, } new->home_node = home_node; - err = mbind_range(mm, vmstart, vmend, new); + err = mbind_range(&vmi, vma, &prev, start, end, new); mpol_put(new); if (err) break;
