The patch titled Subject: mm/mempolicy: fix use-after-free of VMA iterator has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-mempolicy-fix-use-after-free-of-vma-iterator.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: "Liam R. Howlett" Liam.Howlett@oracle.com Subject: mm/mempolicy: fix use-after-free of VMA iterator Date: Mon, 10 Apr 2023 11:22:05 -0400

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@google.com/ Fixes: 66850be55e8e ("mm/mempolicy: use vma iterator & maple state instead of vma linked list") Signed-off-by: Liam R. Howlett Liam.Howlett@oracle.com Reported-by: syzbot+a7c1ec5b1d71ceaa5186@syzkaller.appspotmail.com Link: https://lkml.kernel.org/r/20230410152205.2294819-1-Liam.Howlett@oracle.com Tested-by: syzbot+a7c1ec5b1d71ceaa5186@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/mempolicy.c | 102 ++++++++++++++++++++++------------------------- 1 file changed, 48 insertions(+), 54 deletions(-)

--- a/mm/mempolicy.c~mm-mempolicy-fix-use-after-free-of-vma-iterator +++ a/mm/mempolicy.c @@ -790,61 +790,50 @@ 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) { - VMA_ITERATOR(vmi, mm, 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 = vma_prev(&vmi); - vma = vma_find(&vmi, end); - if (WARN_ON(!vma)) + vmend = min(end, vma->vm_end); + if (start > vma->vm_start) { + *prev = vma; + vmstart = start; + } else { + vmstart = vma->vm_start; + } + + 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(vmi, 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; + return vma_replace_policy(merged, new_pol); + }

- do { - 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(&vmi, 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 = prev; - goto replace; - } - if (vma->vm_start != vmstart) { - err = split_vma(&vmi, vma, vmstart, 1); - if (err) - goto out; - } - if (vma->vm_end != vmend) { - err = split_vma(&vmi, vma, vmend, 0); - if (err) - goto out; - } -replace: - err = vma_replace_policy(vma, new_pol); + if (vma->vm_start != vmstart) { + err = split_vma(vmi, vma, vmstart, 1); if (err) - goto out; -next: - prev = vma; - } for_each_vma_range(vmi, vma, end); + return err; + }

-out: - return err; + if (vma->vm_end != vmend) { + err = split_vma(vmi, vma, vmend, 0); + if (err) + return err; + } + + *prev = vma; + return vma_replace_policy(vma, new_pol); }

/* Set the process memory policy */ @@ -1259,6 +1248,8 @@ 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 +1319,13 @@ 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 +1486,8 @@ 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, *old; - unsigned long vmstart; - unsigned long vmend; unsigned long end; int err = -ENOENT; VMA_ITERATOR(vmi, mm, start); @@ -1521,6 +1516,7 @@ 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) { /* * If any vma in the range got policy other than MPOL_BIND @@ -1541,9 +1537,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, }

new->home_node = home_node; - vmstart = max(start, vma->vm_start); - vmend = min(end, vma->vm_end); - err = mbind_range(mm, vmstart, vmend, new); + err = mbind_range(&vmi, vma, &prev, start, end, new); mpol_put(new); if (err) break; _

Patches currently in -mm which might be from Liam.Howlett@oracle.com are

mm-mprotect-fix-do_mprotect_pkey-return-on-error.patch mm-mempolicy-fix-use-after-free-of-vma-iterator.patch