On 18.10.22 21:17, Liam Howlett wrote:
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.
Just wondering, do we have a simple user space reproducer / test?
Do we want to add some more tests for such scenarios?
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@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/Y06yk66SKxlrwwfb@lakrids/
Link: https://lore.kernel.org/all/20201203085350.22624-1-liuzixian4@xxxxxxxxxx/
Fixes: 4dd1b84140c1 (mm/mmap: use advanced maple tree API for mmap_region())
Reported-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
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;
+ }
If this is something that user space can trigger, WARN_* is the wrong
choice. But what I understand from the comment change is that this must
not happen at that point unless there is a real issue.
Why not "if (WARN_ON_ONCE)" ?
--
Thanks,
David / dhildenb
