Re: [PATCH for v6.3 regression] mm/mremap: fix vm_pgoff in vma_merge() case 3

[Vlastimil Babka <vbabka@suse.cz>]

On 4/27/23 16:09, Vlastimil Babka wrote:
> |later. Alternatively it could be added to mm/mm-stable and upcoming 6.4
> pull request, but then the stable backport would need adjustment. It's up to
> Linus and Andrew. |

This version applies on mm/mm-stable. Paragraph about case 8 is removed
as that case sets vma_pgoff explicitly itself.

----8<----
From dea6d87bdad1fbb21f987dba96c55195fb88e7b4 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Thu, 27 Apr 2023 15:28:41 +0200
Subject: [PATCH] mm/mremap: fix vm_pgoff in vma_merge() case 3

After upgrading build guests to v6.3, rpm started segfaulting for
specific packages, which was bisected to commit 0503ea8f5ba7 ("mm/mmap:
remove __vma_adjust()"). rpm is doing many mremap() operations with file
mappings of its db. The problem is that in vma_merge() case 3 (we merge
with the next vma, expanding it downwards) vm_pgoff is not adjusted as
it should when vm_start changes. As a result the rpm process most likely
sees data from the wrong offset of the file. Fix the vm_pgoff
calculation.

Reported-and-bisected-by: Jiri Slaby <jirislaby@kernel.org>
Reported-and-tested-by: Fabian Vogt <fvogt@suse.com>
Link: https://bugzilla.suse.com/show_bug.cgi?id=1210903
Fixes: 0503ea8f5ba7 ("mm/mmap: remove __vma_adjust()")
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
---
 mm/mmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 536bbb8fa0ae..5522130ae606 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1008,7 +1008,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
 			vma = next;			/* case 3 */
 			vma_start = addr;
 			vma_end = next->vm_end;
-			vma_pgoff = next->vm_pgoff;
+			vma_pgoff = next->vm_pgoff - pglen;
 			if (curr) {			/* case 8 */
 				vma_pgoff = curr->vm_pgoff;
 				remove = curr;
-- 
2.40.0