Messages in this thread Patch in this message | | | From | Johannes Weiner <> | Subject | [PATCH v2] mm: Fix possible off-by-one in walk_pte_range() | Date | Tue, 15 Apr 2008 18:16:53 +0200 |
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Hi,
Mikael Pettersson <mikpe@it.uu.se> writes:
> Johannes Weiner writes: > > After the loop in walk_pte_range() pte might point to the first address > > after the pmd it walks. The pte_unmap() is then applied to something > > bad. > > > > Spotted by Roel Kluin and Andreas Schwab. > > > > Signed-off-by: Johannes Weiner <hannes@saeurebad.de> > > CC: Roel Kluin <12o3l@tiscali.nl> > > CC: Andreas Schwab <schwab@suse.de> > > CC: Matt Mackall <mpm@selenic.com> > > CC: Andrew Morton <akpm@linux-foundation.org> > > --- > > > > A bug is unlikely, though. kunmap_atomic() looks up the kmap entry by > > map-type instead of the address the pte points. So the worst thing I > > could find with a quick grep was that a wrong TLB entry is being > > flushed. Still, the code is wrong :) > > > > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > > index 1cf1417..cf3c004 100644 > > --- a/mm/pagewalk.c > > +++ b/mm/pagewalk.c > > @@ -13,7 +13,7 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, private); > > if (err) > > break; > > - } while (pte++, addr += PAGE_SIZE, addr != end); > > + } while (addr += PAGE_SIZE, addr != end && pte++); > > Instead of obfuscating the code by putting "&& pte++" in the > condition (it will always be true in valid C), you should IMO > rewrite the do-while as a for loop + break, like this: > > for (;;) { > // same body as before > addr += PAGE_SIZE; > if (addr == end) > break; > pte++; > }
Sorry, I think too lispy :)
Hannes ---
From: Johannes Weiner <hannes@saeurebad.de> Subject: [PATCH] mm: Fix possible off-by-one in walk_pte_range()
After the loop in walk_pte_range() pte might point to the first address after the pmd it walks. The pte_unmap() is then applied to something bad.
Spotted by Roel Kluin and Andreas Schwab.
Signed-off-by: Johannes Weiner <hannes@saeurebad.de> CC: Roel Kluin <12o3l@tiscali.nl> CC: Andreas Schwab <schwab@suse.de> CC: Matt Mackall <mpm@selenic.com> CC: Andrew Morton <akpm@linux-foundation.org> ---
A bug is unlikely, though. kunmap_atomic() looks up the kmap entry by map-type instead of the address the pte points. So the worst thing I could find with a quick grep was that a wrong TLB entry is being flushed. Still, the code is wrong :)
diff --git a/mm/pagewalk.c b/mm/pagewalk.c index 1cf1417..0afd238 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -9,11 +9,15 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, int err = 0; pte = pte_offset_map(pmd, addr); - do { + for (;;) { err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, private); if (err) break; - } while (pte++, addr += PAGE_SIZE, addr != end); + addr += PAGE_SIZE; + if (addr == end) + break; + pte++; + } pte_unmap(pte); return err;
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