Merge branch 'core-rslib-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull Reed-Solomon library updates from Thomas Gleixner:
 "A cleanup and fixes series from Ferdinand Blomqvist who analyzed the
  original Reed-Solomon library from Phil Karn on which the kernel
  implementation is based on.

  This comes with a test module which verifies all the various corner
  cases for correctness"

* 'core-rslib-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rslib: Make some functions static
  rslib: Fix remaining decoder flaws
  rslib: Update documentation
  rslib: Fix handling of of caller provided syndrome
  rslib: decode_rs: Code cleanup
  rslib: decode_rs: Fix length parameter check
  rslib: Fix decoding of shortened codes
  rslib: Add tests for the encoder and decoder

lib/Kconfig.debug

@@ -1754,6 +1754,18 @@ config RBTREE_TEST
 	  A benchmark measuring the performance of the rbtree library.
 	  Also includes rbtree invariant checks.
 
+config REED_SOLOMON_TEST
+	tristate "Reed-Solomon library test"
+	depends on DEBUG_KERNEL || m
+	select REED_SOLOMON
+	select REED_SOLOMON_ENC16
+	select REED_SOLOMON_DEC16
+	help
+	  This option enables the self-test function of rslib at boot,
+	  or at module load time.
+
+	  If unsure, say N.
+
 config INTERVAL_TREE_TEST
 	tristate "Interval tree test"
 	depends on DEBUG_KERNEL

lib/reed_solomon/Makefile

@@ -4,4 +4,4 @@
 #
 
 obj-$(CONFIG_REED_SOLOMON) += reed_solomon.o
-
+obj-$(CONFIG_REED_SOLOMON_TEST) += test_rslib.o

lib/reed_solomon/decode_rs.c

@@ -22,6 +22,7 @@
 	uint16_t *index_of = rs->index_of;
 	uint16_t u, q, tmp, num1, num2, den, discr_r, syn_error;
 	int count = 0;
+	int num_corrected;
 	uint16_t msk = (uint16_t) rs->nn;
 
 	/*
@@ -39,11 +40,21 @@
 
 	/* Check length parameter for validity */
 	pad = nn - nroots - len;
-	BUG_ON(pad < 0 || pad >= nn);
+	BUG_ON(pad < 0 || pad >= nn - nroots);
 
 	/* Does the caller provide the syndrome ? */
-	if (s != NULL)
-		goto decode;
+	if (s != NULL) {
+		for (i = 0; i < nroots; i++) {
+			/* The syndrome is in index form,
+			 * so nn represents zero
+			 */
+			if (s[i] != nn)
+				goto decode;
+		}
+
+		/* syndrome is zero, no errors to correct  */
+		return 0;
+	}
 
 	/* form the syndromes; i.e., evaluate data(x) at roots of
 	 * g(x) */
@@ -88,8 +99,7 @@
 		/* if syndrome is zero, data[] is a codeword and there are no
 		 * errors to correct. So return data[] unmodified
 		 */
-		count = 0;
-		goto finish;
+		return 0;
 	}
 
  decode:
@@ -99,9 +109,9 @@
 	if (no_eras > 0) {
 		/* Init lambda to be the erasure locator polynomial */
 		lambda[1] = alpha_to[rs_modnn(rs,
-					      prim * (nn - 1 - eras_pos[0]))];
+					prim * (nn - 1 - (eras_pos[0] + pad)))];
 		for (i = 1; i < no_eras; i++) {
-			u = rs_modnn(rs, prim * (nn - 1 - eras_pos[i]));
+			u = rs_modnn(rs, prim * (nn - 1 - (eras_pos[i] + pad)));
 			for (j = i + 1; j > 0; j--) {
 				tmp = index_of[lambda[j - 1]];
 				if (tmp != nn) {
@@ -175,6 +185,15 @@
 		if (lambda[i] != nn)
 			deg_lambda = i;
 	}
+
+	if (deg_lambda == 0) {
+		/*
+		 * deg(lambda) is zero even though the syndrome is non-zero
+		 * => uncorrectable error detected
+		 */
+		return -EBADMSG;
+	}
+
 	/* Find roots of error+erasure locator polynomial by Chien search */
 	memcpy(&reg[1], &lambda[1], nroots * sizeof(reg[0]));
 	count = 0;		/* Number of roots of lambda(x) */
@@ -188,6 +207,12 @@
 		}
 		if (q != 0)
 			continue;	/* Not a root */
+
+		if (k < pad) {
+			/* Impossible error location. Uncorrectable error. */
+			return -EBADMSG;
+		}
+
 		/* store root (index-form) and error location number */
 		root[count] = i;
 		loc[count] = k;
@@ -202,8 +227,7 @@
 		 * deg(lambda) unequal to number of roots => uncorrectable
 		 * error detected
 		 */
-		count = -EBADMSG;
-		goto finish;
+		return -EBADMSG;
 	}
 	/*
 	 * Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo
@@ -223,7 +247,9 @@
 	/*
 	 * Compute error values in poly-form. num1 = omega(inv(X(l))), num2 =
 	 * inv(X(l))**(fcr-1) and den = lambda_pr(inv(X(l))) all in poly-form
+	 * Note: we reuse the buffer for b to store the correction pattern
 	 */
+	num_corrected = 0;
 	for (j = count - 1; j >= 0; j--) {
 		num1 = 0;
 		for (i = deg_omega; i >= 0; i--) {
@@ -231,6 +257,13 @@
 				num1 ^= alpha_to[rs_modnn(rs, omega[i] +
 							i * root[j])];
 		}
+
+		if (num1 == 0) {
+			/* Nothing to correct at this position */
+			b[j] = 0;
+			continue;
+		}
+
 		num2 = alpha_to[rs_modnn(rs, root[j] * (fcr - 1) + nn)];
 		den = 0;
 
@@ -242,30 +275,52 @@
 						       i * root[j])];
 			}
 		}
-		/* Apply error to data */
-		if (num1 != 0 && loc[j] >= pad) {
-			uint16_t cor = alpha_to[rs_modnn(rs,index_of[num1] +
-						       index_of[num2] +
-						       nn - index_of[den])];
-			/* Store the error correction pattern, if a
-			 * correction buffer is available */
-			if (corr) {
-				corr[j] = cor;
-			} else {
-				/* If a data buffer is given and the
-				 * error is inside the message,
-				 * correct it */
-				if (data && (loc[j] < (nn - nroots)))
-					data[loc[j] - pad] ^= cor;
-			}
+
+		b[j] = alpha_to[rs_modnn(rs, index_of[num1] +
+					       index_of[num2] +
+					       nn - index_of[den])];
+		num_corrected++;
+	}
+
+	/*
+	 * We compute the syndrome of the 'error' and check that it matches
+	 * the syndrome of the received word
+	 */
+	for (i = 0; i < nroots; i++) {
+		tmp = 0;
+		for (j = 0; j < count; j++) {
+			if (b[j] == 0)
+				continue;
+
+			k = (fcr + i) * prim * (nn-loc[j]-1);
+			tmp ^= alpha_to[rs_modnn(rs, index_of[b[j]] + k)];
 		}
+
+		if (tmp != alpha_to[s[i]])
+			return -EBADMSG;
 	}
 
-finish:
-	if (eras_pos != NULL) {
-		for (i = 0; i < count; i++)
-			eras_pos[i] = loc[i] - pad;
+	/*
+	 * Store the error correction pattern, if a
+	 * correction buffer is available
+	 */
+	if (corr && eras_pos) {
+		j = 0;
+		for (i = 0; i < count; i++) {
+			if (b[i]) {
+				corr[j] = b[i];
+				eras_pos[j++] = loc[i] - pad;
+			}
+		}
+	} else if (data && par) {
+		/* Apply error to data and parity */
+		for (i = 0; i < count; i++) {
+			if (loc[i] < (nn - nroots))
+				data[loc[i] - pad] ^= b[i];
+			else
+				par[loc[i] - pad - len] ^= b[i];
+		}
 	}
-	return count;
 
+	return  num_corrected;
 }

lib/reed_solomon/reed_solomon.c

@@ -340,7 +340,8 @@ EXPORT_SYMBOL_GPL(encode_rs8);
  *  @data:	data field of a given type
  *  @par:	received parity data field
  *  @len:	data length
- *  @s:		syndrome data field (if NULL, syndrome is calculated)
+ *  @s: 	syndrome data field, must be in index form
+ *		(if NULL, syndrome is calculated)
  *  @no_eras:	number of erasures
  *  @eras_pos:	position of erasures, can be NULL
  *  @invmsk:	invert data mask (will be xored on data, not on parity!)
@@ -354,7 +355,8 @@ EXPORT_SYMBOL_GPL(encode_rs8);
  *  decoding, so the caller has to ensure that decoder invocations are
  *  serialized.
  *
- *  Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
+ *  Returns the number of corrected symbols or -EBADMSG for uncorrectable
+ *  errors. The count includes errors in the parity.
  */
 int decode_rs8(struct rs_control *rsc, uint8_t *data, uint16_t *par, int len,
 	       uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
@@ -391,7 +393,8 @@ EXPORT_SYMBOL_GPL(encode_rs16);
  *  @data:	data field of a given type
  *  @par:	received parity data field
  *  @len:	data length
- *  @s:		syndrome data field (if NULL, syndrome is calculated)
+ *  @s: 	syndrome data field, must be in index form
+ *		(if NULL, syndrome is calculated)
  *  @no_eras:	number of erasures
  *  @eras_pos:	position of erasures, can be NULL
  *  @invmsk:	invert data mask (will be xored on data, not on parity!)
@@ -403,7 +406,8 @@ EXPORT_SYMBOL_GPL(encode_rs16);
  *  decoding, so the caller has to ensure that decoder invocations are
  *  serialized.
  *
- *  Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
+ *  Returns the number of corrected symbols or -EBADMSG for uncorrectable
+ *  errors. The count includes errors in the parity.
  */
 int decode_rs16(struct rs_control *rsc, uint16_t *data, uint16_t *par, int len,
 		uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,