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mm/mmap: fix MAP_FIXED address return on VMA merge

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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 309d08d9b3
(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: 4dd1b84140 ("mm/mmap: use advanced maple tree API for mmap_region()")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: Mark Rutland <mark.rutland@arm.com>
Cc: Liu Zixian <liuzixian4@huawei.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Liam Howlett 2022-10-18 19:17:12 +00:00 committed by Andrew Morton
parent 1cd916d034
commit a57b70519d
1 changed files with 7 additions and 8 deletions
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15
mm/mmap.c
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@ -2626,14 +2626,14 @@ cannot_expand:
if (error) if (error)
goto unmap_and_free_vma; goto unmap_and_free_vma;
/* Can addr have changed?? /*
* * Expansion is handled above, merging is handled below.
* Answer: Yes, several device drivers can do it in their * Drivers should not alter the address of the VMA.
* f_op->mmap method. -DaveM
*/ */
WARN_ON_ONCE(addr != vma->vm_start); if (WARN_ON((addr != vma->vm_start))) {
error = -EINVAL;
addr = vma->vm_start; goto close_and_free_vma;
}
mas_reset(&mas); mas_reset(&mas);
/* /*
@ -2655,7 +2655,6 @@ cannot_expand:
vm_area_free(vma); vm_area_free(vma);
vma = merge; vma = merge;
/* Update vm_flags to pick up the change. */ /* Update vm_flags to pick up the change. */
addr = vma->vm_start;
vm_flags = vma->vm_flags; vm_flags = vma->vm_flags;
goto unmap_writable; goto unmap_writable;
} }