[PATCH 6.5 028/112] mm/mempolicy: fix set_mempolicy_home_node() previous VMA pointer

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6.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>

commit 51f625377561e5b167da2db5aafb7ee268f691c5 upstream.

The two users of mbind_range() are expecting that mbind_range() will
update the pointer to the previous VMA, or return an error.  However,
set_mempolicy_home_node() does not call mbind_range() if there is no VMA
policy.  The fix is to update the pointer to the previous VMA prior to
continuing iterating the VMAs when there is no policy.

Users may experience a WARN_ON() during VMA policy updates when updating
a range of VMAs on the home node.

Link: https://lkml.kernel.org/r/20230928172432.2246534-1-Liam.Howlett@xxxxxxxxxx
Link: https://lore.kernel.org/linux-mm/CALcu4rbT+fMVNaO_F2izaCT+e7jzcAciFkOvk21HGJsmLcUuwQ@xxxxxxxxxxxxxx/
Fixes: f4e9e0e69468 ("mm/mempolicy: fix use-after-free of VMA iterator")
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Reported-by: Yikebaer Aizezi <yikebaer61@xxxxxxxxx>
Closes: https://lore.kernel.org/linux-mm/CALcu4rbT+fMVNaO_F2izaCT+e7jzcAciFkOvk21HGJsmLcUuwQ@xxxxxxxxxxxxxx/
Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/mempolicy.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1543,8 +1543,10 @@ SYSCALL_DEFINE4(set_mempolicy_home_node,
 		 * the home node for vmas we already updated before.
 		 */
 		old = vma_policy(vma);
-		if (!old)
+		if (!old) {
+			prev = vma;
 			continue;
+		}
 		if (old->mode != MPOL_BIND && old->mode != MPOL_PREFERRED_MANY) {
 			err = -EOPNOTSUPP;
 			break;





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