From ecaaab5649781c5a0effdaf298a925063020500e Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Tue, 28 Nov 2017 20:56:59 -0800
Subject: [PATCH] crypto: salsa20 - fix blkcipher_walk API usage
Git-commit: ecaaab5649781c5a0effdaf298a925063020500e
Patch-mainline: v4.15-rc4
References: CVE-2017-17805,bsc#1073792

When asked to encrypt or decrypt 0 bytes, both the generic and x86
implementations of Salsa20 crash in blkcipher_walk_done(), either when
doing 'kfree(walk->buffer)' or 'free_page((unsigned long)walk->page)',
because walk->buffer and walk->page have not been initialized.

The bug is that Salsa20 is calling blkcipher_walk_done() even when
nothing is in 'walk.nbytes'.  But blkcipher_walk_done() is only meant to
be called when a nonzero number of bytes have been provided.

The broken code is part of an optimization that tries to make only one
call to salsa20_encrypt_bytes() to process inputs that are not evenly
divisible by 64 bytes.  To fix the bug, just remove this "optimization"
and use the blkcipher_walk API the same way all the other users do.

Reproducer: 

    #include <linux/if_alg.h>
    #include <sys/socket.h>
    #include <unistd.h>

    int main()
    {
            int algfd, reqfd;
            struct sockaddr_alg addr = {
                    .salg_type = "skcipher",
                    .salg_name = "salsa20",
            };
            char key[16] = { 0 };

            algfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
            bind(algfd, (void *)&addr, sizeof(addr));
            reqfd = accept(algfd, 0, 0);
            setsockopt(algfd, SOL_ALG, ALG_SET_KEY, key, sizeof(key));
            read(reqfd, key, sizeof(key));
    }

Reported-by: syzbot <syzkaller@googlegroups.com>
Fixes: eb6f13eb9f81 ("[CRYPTO] salsa20_generic: Fix multi-page processing")
Cc: <stable@vger.kernel.org> # v2.6.25+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 arch/x86/crypto/salsa20_glue.c |    7 -------
 crypto/salsa20_generic.c       |    7 -------
 2 files changed, 14 deletions(-)

--- a/arch/x86/crypto/salsa20_glue.c
+++ b/arch/x86/crypto/salsa20_glue.c
@@ -59,13 +59,6 @@ static int encrypt(struct blkcipher_desc
 
 	salsa20_ivsetup(ctx, walk.iv);
 
-	if (likely(walk.nbytes == nbytes))
-	{
-		salsa20_encrypt_bytes(ctx, walk.src.virt.addr,
-				      walk.dst.virt.addr, nbytes);
-		return blkcipher_walk_done(desc, &walk, 0);
-	}
-
 	while (walk.nbytes >= 64) {
 		salsa20_encrypt_bytes(ctx, walk.src.virt.addr,
 				      walk.dst.virt.addr,
--- a/crypto/salsa20_generic.c
+++ b/crypto/salsa20_generic.c
@@ -188,13 +188,6 @@ static int encrypt(struct blkcipher_desc
 
 	salsa20_ivsetup(ctx, walk.iv);
 
-	if (likely(walk.nbytes == nbytes))
-	{
-		salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
-				      walk.src.virt.addr, nbytes);
-		return blkcipher_walk_done(desc, &walk, 0);
-	}
-
 	while (walk.nbytes >= 64) {
 		salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
 				      walk.src.virt.addr,