linux-kernel - [RFT, PATCH v1 1/1] hexdump: truncate output in case of overflow

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Date:	Wed, 28 Oct 2015 12:48:19 +0200
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Aaro Koskinen <aaro.koskinen@...ia.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: [RFT, PATCH v1 1/1] hexdump: truncate output in case of overflow

There is a classical off-by-one error in case when we try to place, for
example, 1+1 bytes as hex in the buffer of size 6. The expected result is to
get an output truncated, but in the reality we get 6 bytes filed followed by
terminating NUL.

Change the logic how we fill the output in case of byte dumping into limited
space. This will follow the snprintf() behaviour by truncating output even on
half bytes.

Fixes: 114fc1afb2de (hexdump: make it return number of bytes placed in buffer)
Reported-by: Aaro Koskinen <aaro.koskinen@...ia.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
Waiting for Aaro's Tested-by: tag, that's why RFT. Meanwhile I will update
test-hexdump to cover all corner case in overflow.

Linus, it would be nice to promote the fix when we get Aaro's confirmation.

 lib/hexdump.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/hexdump.c b/lib/hexdump.c
index 8d74c20..992457b 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -169,11 +169,15 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 		}
 	} else {
 		for (j = 0; j < len; j++) {
-			if (linebuflen < lx + 3)
+			if (linebuflen < lx + 2)
 				goto overflow2;
 			ch = ptr[j];
 			linebuf[lx++] = hex_asc_hi(ch);
+			if (linebuflen < lx + 2)
+				goto overflow2;
 			linebuf[lx++] = hex_asc_lo(ch);
+			if (linebuflen < lx + 2)
+				goto overflow2;
 			linebuf[lx++] = ' ';
 		}
 		if (j)
-- 
2.6.1

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