linux-kernel - [105/121] SUNRPC: Fix memory corruption issue on 32-bit highmem systems

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Message-ID: <lsq.1378608721.901404264@decadent.org.uk>
Date:	Sun, 08 Sep 2013 03:52:01 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Matt Craighead" <mcraighead@...dia.com>,
	"Trond Myklebust" <Trond.Myklebust@...app.com>,
	"Mark Young" <MYoung@...dia.com>,
	"Bruce Fields" <bfields@...ldses.org>
Subject: [105/121] SUNRPC: Fix memory corruption issue on 32-bit highmem
 systems

3.2.51-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Trond Myklebust <Trond.Myklebust@...app.com>

commit 347e2233b7667e336d9f671f1a52dfa3f0416e2c upstream.

Some architectures, such as ARM-32 do not return the same base address
when you call kmap_atomic() twice on the same page.
This causes problems for the memmove() call in the XDR helper routine
"_shift_data_right_pages()", since it defeats the detection of
overlapping memory ranges, and has been seen to corrupt memory.

The fix is to distinguish between the case where we're doing an
inter-page copy or not. In the former case of we know that the memory
ranges cannot possibly overlap, so we can additionally micro-optimise
by replacing memmove() with memcpy().

Reported-by: Mark Young <MYoung@...dia.com>
Reported-by: Matt Craighead <mcraighead@...dia.com>
Cc: Bruce Fields <bfields@...ldses.org>
Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
Tested-by: Matt Craighead <mcraighead@...dia.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/sunrpc/xdr.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -233,10 +233,13 @@ _shift_data_right_pages(struct page **pa
 		pgfrom_base -= copy;
 
 		vto = kmap_atomic(*pgto);
-		vfrom = kmap_atomic(*pgfrom);
-		memmove(vto + pgto_base, vfrom + pgfrom_base, copy);
+		if (*pgto != *pgfrom) {
+			vfrom = kmap_atomic(*pgfrom);
+			memcpy(vto + pgto_base, vfrom + pgfrom_base, copy);
+			kunmap_atomic(vfrom);
+		} else
+			memmove(vto + pgto_base, vto + pgfrom_base, copy);
 		flush_dcache_page(*pgto);
-		kunmap_atomic(vfrom);
 		kunmap_atomic(vto);
 
 	} while ((len -= copy) != 0);

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