[PATCH 2/7] crypto: Fixes uninitialized skcipher_walk use in des3_ede_glue

[Yuran Pereira <yuran.pereira@hotmail.com>]

In the following functions:
 - `ecb_crypt`
 - `cbc_encrypt`
 - `cbc_decrypt`

`struct skcipher_walk *walk` is not fully initialized before its use.

Although the call to `skcipher_walk_virt()` and subsequent functions
that this function calls seem to initialize some fields of this struct,

there is a chance that `skcipher_walk_virt()` returns
without fully clearing or properly initializing the `->flags` field
which means that the following flags:
`SKCIPHER_WALK_DIFF`, `SKCIPHER_WALK_COPY`, `SKCIPHER_WALK_SLOW`
could be storing junk values by the time `skcipher_walk_done()` is called.

This could lead to buggy or undefined behaviour since these flags
are checked in `skcipher_walk_done()`:

```C
int skcipher_walk_done(struct skcipher_walk *walk, int err)
{
	...
    if (likely(!(walk->flags & (SKCIPHER_WALK_PHYS |
        SKCIPHER_WALK_SLOW |
        SKCIPHER_WALK_COPY |
        SKCIPHER_WALK_DIFF)))) {
    ...
}
```

To prevent this, this patch ensures that instances of
`struct skcipher_walk` are correctly initialized prior to their use.

Addresses-Coverity-IDs: 1434673 ("Unintialized scalar variable")
Signed-off-by: Yuran Pereira <yuran.pereira@hotmail.com>
---
 arch/x86/crypto/des3_ede_glue.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/crypto/des3_ede_glue.c b/arch/x86/crypto/des3_ede_glue.c
index abb8b1fe123b..6f16b09b52fe 100644
--- a/arch/x86/crypto/des3_ede_glue.c
+++ b/arch/x86/crypto/des3_ede_glue.c
@@ -15,6 +15,7 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/types.h>
+#include <linux/string.h>
 
 struct des3_ede_x86_ctx {
 	struct des3_ede_ctx enc;
@@ -70,6 +71,7 @@ static int ecb_crypt(struct skcipher_request *req, const u32 *expkey)
 	unsigned int nbytes;
 	int err;
 
+	memset(&walk, 0, sizeof(walk));
 	err = skcipher_walk_virt(&walk, req, false);
 
 	while ((nbytes = walk.nbytes)) {
@@ -154,6 +156,7 @@ static int cbc_encrypt(struct skcipher_request *req)
 	unsigned int nbytes;
 	int err;
 
+	memset(&walk, 0, sizeof(walk));
 	err = skcipher_walk_virt(&walk, req, false);
 
 	while (walk.nbytes) {
@@ -233,6 +236,7 @@ static int cbc_decrypt(struct skcipher_request *req)
 	unsigned int nbytes;
 	int err;
 
+	memset(&walk, 0, sizeof(walk));
 	err = skcipher_walk_virt(&walk, req, false);
 
 	while (walk.nbytes) {
-- 
2.25.1