linux-kernel - [PATCH v5] hexdump: fix for non-aligned buffers

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Date:	Tue, 14 Jul 2015 00:23:20 +0200
From:	Horacio Mijail Anton Quiles <hmijail@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	David Howells <dhowells@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	trivial@...nel.org, Joe Perches <joe@...ches.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH v5] hexdump: fix for non-aligned buffers

An hexdump with a buf not aligned to the groupsize causes
non-naturally-aligned memory accesses. This was causing a kernel panic
on the processor BlackFin BF527, when such an unaligned buffer was fed
by the function ubifs_scanned_corruption in fs/ubifs/scan.c .

To fix this, change accesses to the contents of the buffer so they go
through get_unaligned(). This change should be harmless to unaligned-
access-capable architectures, and any performance hit should be anyway
dwarfed by the snprintf() processing time.

Signed-off-by: Horacio Mijail Antón Quiles <hmijail@...il.com>
---
Changes in v5:
 - Instead of trying to detect non-unaligned-capable architectures,
     change all accesses to unconditionally use get_unaligned() (per
     Andrew Morton's and Geert Uytterhoeven's comments)

Changes in v4:
 - Added space before "*/" (per Joe Perches' indication)

Changes in v3:
 - Removed trailing whitespace (per Joe Perches' indication)
 - Changed mail headers to avoid encoding issues (per Joe Perches' hint)

Changes in v2:
 - Changed from ad-hoc calculation to IS_ALIGNED() for readability (per
     Joe Perches' indication)
 - Made the explanation clearer (aligned vs naturally aligned)

---
 lib/hexdump.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/hexdump.c b/lib/hexdump.c
index 7ea0969..e3af13c 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -11,6 +11,7 @@
 #include <linux/ctype.h>
 #include <linux/kernel.h>
 #include <linux/export.h>
+#include <asm/unaligned.h>
 
 const char hex_asc[] = "0123456789abcdef";
 EXPORT_SYMBOL(hex_asc);
@@ -139,7 +140,8 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 		for (j = 0; j < ngroups; j++) {
 			ret = snprintf(linebuf + lx, linebuflen - lx,
 				       "%s%16.16llx", j ? " " : "",
-				       (unsigned long long)*(ptr8 + j));
+				       (unsigned long long)
+					       get_unaligned(ptr8 + j));
 			if (ret >= linebuflen - lx)
 				goto overflow1;
 			lx += ret;
@@ -150,7 +152,7 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 		for (j = 0; j < ngroups; j++) {
 			ret = snprintf(linebuf + lx, linebuflen - lx,
 				       "%s%8.8x", j ? " " : "",
-				       *(ptr4 + j));
+				       get_unaligned(ptr4 + j));
 			if (ret >= linebuflen - lx)
 				goto overflow1;
 			lx += ret;
@@ -161,7 +163,7 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 		for (j = 0; j < ngroups; j++) {
 			ret = snprintf(linebuf + lx, linebuflen - lx,
 				       "%s%4.4x", j ? " " : "",
-				       *(ptr2 + j));
+				       get_unaligned(ptr2 + j));
 			if (ret >= linebuflen - lx)
 				goto overflow1;
 			lx += ret;
-- 
2.1.4

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