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/mm-mempolicy-fix-use-after-free-of-vma-iterator.patch
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@xxxxxxxxxx>
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@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>
---
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@xxxxxxxxxx are
mm-mprotect-fix-do_mprotect_pkey-return-on-error.patch
mm-mempolicy-fix-use-after-free-of-vma-iterator.patch
