Commit message: lz4: ensure length does not wrap

Given some pathologically compressed data, lz4 could possibly decide to
wrap a few internal variables, causing unknown things to happen.  Catch
this before the wrapping happens and abort the decompression.

Reported-by: "Don A. Bailey" <donb@securitymouse.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CVE: CVE-2014-4611
CWE: CWE-20
Vulnerability description: Integer overflow in the LZ4 algorithm implementation, as used in Yann Collet LZ4 before r118 and in the lz4_uncompress function in lib/lz4/lz4_decompress.c in the Linux kernel before 3.15.2, on 32-bit platforms might allow context-dependent attackers to cause a denial of service (memory corruption) or possibly have unspecified other impact via a crafted Literal Run that would be improperly handled by programs not complying with an API limitation, a different vulnerability than CVE-2014-4715.

Project: linux

static int lz4_uncompress(const char *source, char *dest, int osize)
{
	const BYTE *ip = (const BYTE *) source;
	const BYTE *ref;
	BYTE *op = (BYTE *) dest;
	BYTE * const oend = op + osize;
	BYTE *cpy;
	unsigned token;
	size_t length;
	size_t dec32table[] = {0, 3, 2, 3, 0, 0, 0, 0};
#if LZ4_ARCH64
	size_t dec64table[] = {0, 0, 0, -1, 0, 1, 2, 3};
#endif

	while (1) {

		/* get runlength */
		token = *ip++;
		length = (token >> ML_BITS);
		if (length == RUN_MASK) {
			size_t len;

 			len = *ip++;
 			for (; len == 255; length += 255)
 				len = *ip++;
 			length += len;
 		}
 
		/* copy literals */
		cpy = op + length;
		if (unlikely(cpy > oend - COPYLENGTH)) {
			/*
			 * Error: not enough place for another match
			 * (min 4) + 5 literals
			 */
			if (cpy != oend)
				goto _output_error;

			memcpy(op, ip, length);
			ip += length;
			break; /* EOF */
		}
		LZ4_WILDCOPY(ip, op, cpy);
		ip -= (op - cpy);
		op = cpy;

		/* get offset */
		LZ4_READ_LITTLEENDIAN_16(ref, cpy, ip);
		ip += 2;

		/* Error: offset create reference outside destination buffer */
		if (unlikely(ref < (BYTE *const) dest))
			goto _output_error;

		/* get matchlength */
		length = token & ML_MASK;
		if (length == ML_MASK) {
			for (; *ip == 255; length += 255)
				ip++;
			length += *ip++;
		}

		/* copy repeated sequence */
		if (unlikely((op - ref) < STEPSIZE)) {
#if LZ4_ARCH64
			size_t dec64 = dec64table[op - ref];
#else
			const int dec64 = 0;
#endif
			op[0] = ref[0];
			op[1] = ref[1];
			op[2] = ref[2];
			op[3] = ref[3];
			op += 4;
			ref += 4;
			ref -= dec32table[op-ref];
			PUT4(ref, op);
			op += STEPSIZE - 4;
			ref -= dec64;
		} else {
			LZ4_COPYSTEP(ref, op);
		}
		cpy = op + length - (STEPSIZE - 4);
		if (cpy > (oend - COPYLENGTH)) {

			/* Error: request to write beyond destination buffer */
			if (cpy > oend)
				goto _output_error;
			LZ4_SECURECOPY(ref, op, (oend - COPYLENGTH));
			while (op < cpy)
				*op++ = *ref++;
			op = cpy;
			/*
			 * Check EOF (should never happen, since last 5 bytes
			 * are supposed to be literals)
			 */
			if (op == oend)
				goto _output_error;
			continue;
		}
		LZ4_SECURECOPY(ref, op, cpy);
		op = cpy; /* correction */
	}
	/* end of decoding */
	return (int) (((char *)ip) - source);

	/* write overflow error detected */
_output_error:
	return (int) (-(((char *)ip) - source));
}