[PATCH] crypto: chacha20poly1305 - Fix missing state zeroization in xchacha decrypt

[Mohamad Raizudeen <raizudeen.kerneldev@gmail.com>]

The `__chacha20poly1305_decrypt` function does not zeroize the chacha
state, unlike its encrypt counterpart. The regular
`chacha20poly1305_decrypt` function handles this by manually calling
chacha_zeroize_state(). However, `xchacha20poly1305_decrypt` returns
the result directly without clearing the state.

This leaves the derived chacha20 subkey on the stack after the function
returns. Fix this by storing the return value, calling
chacha_zeroize_state() and then returning the result, matching the
logic in `chacha20poly1305_decrypt`.

Fixes: ed20078b7e333 ("crypto: chacha20poly1305 - import construction and selftest from Zinc")
Cc: stable@vger.kernel.org
Signed-off-by: Mohamad Raizudeen <raizudeen.kerneldev@gmail.com>
---
 lib/crypto/chacha20poly1305.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/crypto/chacha20poly1305.c b/lib/crypto/chacha20poly1305.c
index ea42a28f4ff7..03b14d272520 100644
--- a/lib/crypto/chacha20poly1305.c
+++ b/lib/crypto/chacha20poly1305.c
@@ -199,10 +199,13 @@ bool xchacha20poly1305_decrypt(u8 *dst, const u8 *src, const size_t src_len,
 			       const u8 key[at_least CHACHA20POLY1305_KEY_SIZE])
 {
 	struct chacha_state chacha_state;
+	bool ret;
 
 	xchacha_init(&chacha_state, key, nonce);
-	return __chacha20poly1305_decrypt(dst, src, src_len, ad, ad_len,
+	ret = __chacha20poly1305_decrypt(dst, src, src_len, ad, ad_len,
 					  &chacha_state);
+	chacha_zeroize_state(&chacha_state);
+	return ret;
 }
 EXPORT_SYMBOL(xchacha20poly1305_decrypt);
 
-- 
2.53.0