[PATCH v2] lib: Verify array index is correct before using it

[Huang Guobin]

This code reads from the array before verifying that "c" is a valid
index. Move test array offset code before use to fix it.

Fixes: 2da572c959dd ("lib: add software 842 compression/decompression")
Signed-off-by: Huang Guobin <huangguobin4@xxxxxxxxxx>
---
 lib/842/842_compress.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/842/842_compress.c b/lib/842/842_compress.c
index c02baa4168e1..c37bfe0b9346 100644
--- a/lib/842/842_compress.c
+++ b/lib/842/842_compress.c
@@ -11,6 +11,7 @@
 #define MODULE_NAME "842_compress"
 
 #include <linux/hashtable.h>
+#include <linux/nospec.h>
 
 #include "842.h"
 #include "842_debugfs.h"
@@ -222,12 +223,14 @@ static int add_bits(struct sw842_param *p, u64 d, u8 n)
 static int add_template(struct sw842_param *p, u8 c)
 {
 	int ret, i, b = 0;
-	u8 *t = comp_ops[c];
+	u8 *t = NULL;
 	bool inv = false;
 
 	if (c >= OPS_MAX)
 		return -EINVAL;
+	c = array_index_nospec(c, OPS_MAX);
 
+	t = comp_ops[c];
 	pr_debug("template %x\n", t[4]);
 
 	ret = add_bits(p, t[4], OP_BITS);
@@ -379,12 +382,14 @@ static int add_end_template(struct sw842_param *p)
 
 static bool check_template(struct sw842_param *p, u8 c)
 {
-	u8 *t = comp_ops[c];
+	u8 *t = NULL;
 	int i, match, b = 0;
 
 	if (c >= OPS_MAX)
 		return false;
+	c = array_index_nospec(c, OPS_MAX);
 
+	t = comp_ops[c];
 	for (i = 0; i < 4; i++) {
 		if (t[i] & OP_ACTION_INDEX) {
 			if (t[i] & OP_AMOUNT_2)
-- 
2.17.1