[PATCH URGENT crypto v2] crypto: arm64/chacha - correctly walk through blocks

[Jason A. Donenfeld]

Prior, passing in chunks of 2, 3, or 4, followed by any additional
chunks would result in the chacha state counter getting out of sync,
resulting in incorrect encryption/decryption, which is a pretty nasty
crypto vuln: "why do images look weird on webpages?" WireGuard users
never experienced this prior, because we have always, out of tree, used
a different crypto library, until the recent Frankenzinc addition. This
commit fixes the issue by advancing the pointers and state counter by
the actual size processed. It also fixes up a bug in the (optional,
costly) stride test that prevented it from running on arm64.

Fixes: b3aad5bad26a ("crypto: arm64/chacha - expose arm64 ChaCha routine as library function")
Reported-and-tested-by: Emil Renner Berthing <kernel@xxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.5+
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
---
 arch/arm64/crypto/chacha-neon-glue.c   |  8 ++++----
 lib/crypto/chacha20poly1305-selftest.c | 11 ++++++++---
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/crypto/chacha-neon-glue.c b/arch/arm64/crypto/chacha-neon-glue.c
index c1f9660d104c..37ca3e889848 100644
--- a/arch/arm64/crypto/chacha-neon-glue.c
+++ b/arch/arm64/crypto/chacha-neon-glue.c
@@ -55,10 +55,10 @@ static void chacha_doneon(u32 *state, u8 *dst, const u8 *src,
 			break;
 		}
 		chacha_4block_xor_neon(state, dst, src, nrounds, l);
-		bytes -= CHACHA_BLOCK_SIZE * 5;
-		src += CHACHA_BLOCK_SIZE * 5;
-		dst += CHACHA_BLOCK_SIZE * 5;
-		state[12] += 5;
+		bytes -= l;
+		src += l;
+		dst += l;
+		state[12] += DIV_ROUND_UP(l, CHACHA_BLOCK_SIZE);
 	}
 }
 
diff --git a/lib/crypto/chacha20poly1305-selftest.c b/lib/crypto/chacha20poly1305-selftest.c
index c391a91364e9..fa43deda2660 100644
--- a/lib/crypto/chacha20poly1305-selftest.c
+++ b/lib/crypto/chacha20poly1305-selftest.c
@@ -9028,10 +9028,15 @@ bool __init chacha20poly1305_selftest(void)
 	     && total_len <= 1 << 10; ++total_len) {
 		for (i = 0; i <= total_len; ++i) {
 			for (j = i; j <= total_len; ++j) {
+				k = 0;
 				sg_init_table(sg_src, 3);
-				sg_set_buf(&sg_src[0], input, i);
-				sg_set_buf(&sg_src[1], input + i, j - i);
-				sg_set_buf(&sg_src[2], input + j, total_len - j);
+				if (i)
+					sg_set_buf(&sg_src[k++], input, i);
+				if (j - i)
+					sg_set_buf(&sg_src[k++], input + i, j - i);
+				if (total_len - j)
+					sg_set_buf(&sg_src[k++], input + j, total_len - j);
+				sg_init_marker(sg_src, k);
 				memset(computed_output, 0, total_len);
 				memset(input, 0, total_len);
 
-- 
2.25.1