From a57b70519d1f7c53be98478623652738e5ac70d5 Mon Sep 17 00:00:00 2001 From: Liam Howlett Date: Tue, 18 Oct 2022 19:17:12 +0000 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. Link: https://lkml.kernel.org/r/20221018191613.4133459-1-Liam.Howlett@oracle.com 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()") Signed-off-by: Liam R. Howlett Reported-by: Mark Rutland Cc: Liu Zixian Cc: David Hildenbrand Cc: Jason Gunthorpe Cc: Matthew Wilcox Signed-off-by: Andrew Morton --- mm/mmap.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 721fe5c82a0e..e270057ed04e 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2626,14 +2626,14 @@ cannot_expand: 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); /* @@ -2655,7 +2655,6 @@ cannot_expand: 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; }