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Message-ID: <20221018191613.4133459-1-Liam.Howlett@oracle.com>
Date: Tue, 18 Oct 2022 19:17:12 +0000
From: Liam Howlett <liam.howlett@...cle.com>
To: "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
CC: Liam Howlett <liam.howlett@...cle.com>,
Liu Zixian <liuzixian4@...wei.com>,
David Hildenbrand <david@...hat.com>,
Jason Gunthorpe <jgg@...dia.com>,
Matthew Wilcox <willy@...radead.org>,
Mark Rutland <mark.rutland@....com>
Subject: [PATCH] mm/mmap: Fix MAP_FIXED address return on VMA merge
mmap should return the start address of newly mapped area when
successful. On a successful merge of a VMA, the return address was
changed and thus was violating that expectation from userspace.
This is a restoration of functionality provided by 309d08d9b3a3
(mm/mmap.c: fix mmap return value when vma is merged after call_mmap()).
For completeness of fixing MAP_FIXED, implement the comments from the
previous discussion to never update the address and fail if the address
changes. Leaving the error as a WARN_ON() to avoid crashing the kernel.
Cc: Liu Zixian <liuzixian4@...wei.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Jason Gunthorpe <jgg@...dia.com>
Cc: Matthew Wilcox <willy@...radead.org>
Link: https://lore.kernel.org/all/Y06yk66SKxlrwwfb@lakrids/
Link: https://lore.kernel.org/all/20201203085350.22624-1-liuzixian4@huawei.com/
Fixes: 4dd1b84140c1 (mm/mmap: use advanced maple tree API for mmap_region())
Reported-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
mm/mmap.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 42cd2c260898..22010e13f1a1 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2625,14 +2625,14 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (error)
goto unmap_and_free_vma;
- /* Can addr have changed??
- *
- * Answer: Yes, several device drivers can do it in their
- * f_op->mmap method. -DaveM
+ /*
+ * Expansion is handled above, merging is handled below.
+ * Drivers should not alter the address of the VMA.
*/
- WARN_ON_ONCE(addr != vma->vm_start);
-
- addr = vma->vm_start;
+ if (WARN_ON((addr != vma->vm_start))) {
+ error = -EINVAL;
+ goto close_and_free_vma;
+ }
mas_reset(&mas);
/*
@@ -2654,7 +2654,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
vm_area_free(vma);
vma = merge;
/* Update vm_flags to pick up the change. */
- addr = vma->vm_start;
vm_flags = vma->vm_flags;
goto unmap_writable;
}
--
2.35.1
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