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UPSTREAM: mm/mremap.c: fix extent calculation

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When `next < old_addr`, `next - old_addr` arithmetic underflows causing
`extent` to be incorrect.

Make `extent` the smaller of `next - old_addr` or `old_end - old_addr`.

Link: https://lkml.kernel.org/r/20201219170433.2418867-1-kaleshsingh@google.com
Fixes: c49dd34018026 ("mm: speedup mremap on 1GB or larger regions")
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit e05986ee7a5814bec0e0075d813daca3d46e4a9e)

Bug: 151772539
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Change-Id: Ibcbd39dfa16f8ebd1aeca469540b0ef43fb849c9
This commit is contained in:
Kalesh Singh 2020-12-29 15:14:40 -08:00 • committed by Michael Bestas
commit b254e3e87d
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GPG key ID: CC95044519BE6669
1 changed files with 3 additions and 1 deletions
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4
mm/mremap.c
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@ -385,7 +385,9 @@ static unsigned long get_extent(enum pgt_entry entry, unsigned long old_addr,
next = (old_addr + size) & mask;
/* even if next overflowed, extent below will be ok */
extent = (next > old_end) ? old_end - old_addr : next - old_addr;
extent = next - old_addr;
if (extent > old_end - old_addr)
extent = old_end - old_addr;
next = (new_addr + size) & mask;
if (extent > next - new_addr)
extent = next - new_addr;