[tip:core/rslib] rslib: Fix handling of of caller provided syndrome

[tip-bot for Ferdinand Blomqvist]

Commit-ID:  ef4d6a8556b637ad27c8c2a2cff1dda3da38e9a9
Gitweb:     https://git.kernel.org/tip/ef4d6a8556b637ad27c8c2a2cff1dda3da38e9a9
Author:     Ferdinand Blomqvist <ferdinand.blomqvist@xxxxxxxxx>
AuthorDate: Thu, 20 Jun 2019 17:10:37 +0300
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 26 Jun 2019 14:55:47 +0200

rslib: Fix handling of of caller provided syndrome

Check if the syndrome provided by the caller is zero, and act
accordingly.

Signed-off-by: Ferdinand Blomqvist <ferdinand.blomqvist@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190620141039.9874-6-ferdinand.blomqvist@xxxxxxxxx

---
 lib/reed_solomon/decode_rs.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/lib/reed_solomon/decode_rs.c b/lib/reed_solomon/decode_rs.c
index 78629bbe6590..b7264a712d46 100644
--- a/lib/reed_solomon/decode_rs.c
+++ b/lib/reed_solomon/decode_rs.c
@@ -42,8 +42,18 @@
 	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) */