[PATCH 3/7] crypto: Fixes uninitialized skcipher_walk use in chacha_glue

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

In `chacha_simd_stream_xor()`, `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: 1456799 ("Unintialized scalar variable")
Signed-off-by: Yuran Pereira <yuran.pereira@hotmail.com>
---
 arch/x86/crypto/chacha_glue.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/crypto/chacha_glue.c b/arch/x86/crypto/chacha_glue.c
index 7b3a1cf0984b..be8dc756d205 100644
--- a/arch/x86/crypto/chacha_glue.c
+++ b/arch/x86/crypto/chacha_glue.c
@@ -13,6 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/sizes.h>
+#include <linux/string.h>
 #include <asm/simd.h>
 
 asmlinkage void chacha_block_xor_ssse3(u32 *state, u8 *dst, const u8 *src,
@@ -167,6 +168,7 @@ static int chacha_simd_stream_xor(struct skcipher_request *req,
 	struct skcipher_walk walk;
 	int err;
 
+	memset(&walk, 0, sizeof(walk));
 	err = skcipher_walk_virt(&walk, req, false);
 
 	chacha_init_generic(state, ctx->key, iv);
-- 
2.25.1