hexdump: fix for non-naturally-aligned buffers

PATCH Superseded =?UTF-8?q?Horacio=20Mijail=20Ant=C3=B3n=20Quiles?= 2 participants 2 messages Jun 21, 2015 Library code

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2015-06-21 16:37 UTC #0 lore raw

PATCH 1/1 hexdump: fix for non-naturally-aligned buffers

Calling hex_dump_to_buffer() with a buffer non-naturally-aligned to the groupsize causes non-naturally-aligned memory accesses. This was causing a kernel panic on the BlackFin BF527, when such a call was made by ubifs_scanned_corruption() in fs/ubifs/scan.c .

To fix this, if the buffer is non-naturally aligned in a platform which does not define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, then change the groupsize to 1, so alignment is no longer a problem.
This behavior is coherent with the way the function currently deals with inappropriate parameter combinations, which is to fall back to safe "defaults", even if that means changing the output format and the implicit access patterns that could have been expected.

Signed-off-by Horacio Mijail Antón Quiles <[email protected]>

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

lib/hexdump.c +5 -0

index 7ea0969..ba9f384 100644
@@ -123,6 +123,11 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 		groupsize = 1;
 	if ((len % groupsize) != 0)	/* no mixed size output */
 		groupsize = 1;
+	
+	/* fall back to 1-byte groups if buf is not naturally aligned */
+	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
+	    (((uintptr_t)buf % groupsize) != 0))
+		groupsize = 1;
 
 	ngroups = len / groupsize;
 	ascii_column = rowsize * 2 + rowsize / groupsize + 1;

Signature · 5 lines

2.1.4

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Joe Perches

2015-06-21 16:47 UTC #1 lore raw

Quoted 4 lines · On Sun, 2015-06-21 at 18:36 +0200, =?UTF-8?q?Horacio=20Mijail=20Ant=C3=B3n=20Qu…

Calling hex_dump_to_buffer() with a buffer non-naturally-aligned to the groupsize causes non-naturally-aligned memory accesses. This was causing a kernel panic on the BlackFin BF527, when such a call was made by ubifs_scanned_corruption() in fs/ubifs/scan.c .

[]

lib/hexdump.c

Quoted 1 line

lib/hexdump.c +0 -0

[]

lib/hexdump.c int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize, · line 130

Quoted 9 lines

lib/hexdump.c +5 -0

@@ -123,6 +123,11 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 		groupsize = 1;
 	if ((len % groupsize) != 0)	/* no mixed size output */
 		groupsize = 1;
+	
+	/* fall back to 1-byte groups if buf is not naturally aligned */
+	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
+	    (((uintptr_t)buf % groupsize) != 0))
+		groupsize = 1;

Maybe !IS_ALIGNED(buf, groupsize) reads better.

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