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mm/mempolicy: fix use-after-free of VMA iterator
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commit f4e9e0e 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@google.com/
Fixes: 66850be ("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>
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@howlett @gregkh
howlett authored and gregkh committed Apr 30, 2023
1 parent e1562cc commit 862ea63
Showing 1 changed file with 53 additions and 62 deletions.
115 changes: 53 additions & 62 deletions mm/mempolicy.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -784,70 +784,56 @@ static int vma_replace_policy(struct vm_area_struct *vma,
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;

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);
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);
}

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 */
Expand Down Expand Up @@ -1259,6 +1245,8 @@ static long do_mbind(unsigned long start, unsigned long len,
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;
Expand Down Expand Up @@ -1328,7 +1316,13 @@ static long do_mbind(unsigned long start, unsigned long len,
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;
Expand Down Expand Up @@ -1489,10 +1483,8 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
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);
Expand Down Expand Up @@ -1521,9 +1513,8 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
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);
Expand All @@ -1547,7 +1538,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
}

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;
Expand Down

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