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Subject[01/70] vm: fix vm_pgoff wrap in stack expansion
2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Linus Torvalds <torvalds@linux-foundation.org>

commit a626ca6a656450e9f4df91d0dda238fff23285f4 upstream.

Commit 982134ba6261 ("mm: avoid wrapping vm_pgoff in mremap()") fixed
the case of a expanding mapping causing vm_pgoff wrapping when you used
mremap. But there was another case where we expand mappings hiding in
plain sight: the automatic stack expansion.

This fixes that case too.

This one also found by Robert Święcki, using his nasty system call
fuzzer tool. Good job.

Reported-and-tested-by: Robert Święcki <robert@swiecki.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
mm/mmap.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1814,11 +1814,14 @@ static int expand_downwards(struct vm_ar
size = vma->vm_end - address;
grow = (vma->vm_start - address) >> PAGE_SHIFT;

- error = acct_stack_growth(vma, size, grow);
- if (!error) {
- vma->vm_start = address;
- vma->vm_pgoff -= grow;
- perf_event_mmap(vma);
+ error = -ENOMEM;
+ if (grow <= vma->vm_pgoff) {
+ error = acct_stack_growth(vma, size, grow);
+ if (!error) {
+ vma->vm_start = address;
+ vma->vm_pgoff -= grow;
+ perf_event_mmap(vma);
+ }
}
}
vma_unlock_anon_vma(vma);

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