mm/mseal: update VMA end correctly on merge

Previously we stored the end of the current VMA in curr_end, and then upon
iterating to the next VMA updated curr_start to curr_end to advance to the
next VMA.

However, this doesn't take into account the fact that a VMA might be
updated due to a merge by vma_modify_flags(), which can result in curr_end
being stale and thus, upon setting curr_start to curr_end, ending up with
an incorrect curr_start on the next iteration.

Resolve the issue by setting curr_end to vma->vm_end unconditionally to
ensure this value remains updated should this occur.

While we're here, eliminate this entire class of bug by simply setting
const curr_[start/end] to be clamped to the input range and VMAs, which
also happens to simplify the logic.

Link: https://lkml.kernel.org/r/20260327173104.322405-1-ljs@kernel.org
Fixes: 6c2da14ae1e0 ("mm/mseal: rework mseal apply logic")
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Reported-by: Antonius <antonius@bluedragonsec.com>
Closes: https://lore.kernel.org/linux-mm/CAK8a0jwWGj9-SgFk0yKFh7i8jMkwKm5b0ao9=kmXWjO54veX2g@mail.gmail.com/
Suggested-by: David Hildenbrand (ARM) <david@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mseal.c b/mm/mseal.c
index 316b5e1dec7818ed48446cbae3042d0ade341070..ac58643181f7850847259da3bc344edfe31b6f52 100644 (file)
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -56,7 +56,6 @@ static int mseal_apply(struct mm_struct *mm,
                unsigned long start, unsigned long end)
 {
        struct vm_area_struct *vma, *prev;
-       unsigned long curr_start = start;
        VMA_ITERATOR(vmi, mm, start);
 
        /* We know there are no gaps so this will be non-NULL. */
@@ -66,6 +65,7 @@ static int mseal_apply(struct mm_struct *mm,
                prev = vma;
 
        for_each_vma_range(vmi, vma, end) {
+               const unsigned long curr_start = MAX(vma->vm_start, start);
                const unsigned long curr_end = MIN(vma->vm_end, end);
 
                if (!(vma->vm_flags & VM_SEALED)) {
@@ -79,7 +79,6 @@ static int mseal_apply(struct mm_struct *mm,
                }
 
                prev = vma;
-               curr_start = curr_end;
        }
 
        return 0;