[PATCH] crypto: cbc - Ensure statesize is zero

[Herbert Xu]

On Mon, Jan 29, 2024 at 04:55:30AM -0800, syzbot wrote:
> 
> HEAD commit:    3a5879d495b2 Merge tag 'ata-6.8-rc2' of git://git.kernel.o..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1683b6bbe80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bc36d99546fe9035
> dashboard link: https://syzkaller.appspot.com/bug?extid=050eeedd6c285d8c42f2

Thanks for the report.  This is actually caused by the construction
of cbc(arc4), which wasn't possible previously.  Let's make it
impossible again:

---8<---
The cbc template should not be applied on stream ciphers, especially
ones that have internal state.  Enforce this by checking the state
size when the instance is created.

Reported-by: syzbot+050eeedd6c285d8c42f2@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 47309ea13591 ("crypto: arc4 - Add internal state")
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

diff --git a/crypto/cbc.c b/crypto/cbc.c
index eedddef9ce40..e81918ca68b7 100644
--- a/crypto/cbc.c
+++ b/crypto/cbc.c
@@ -148,6 +148,9 @@ static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb)
 	if (!is_power_of_2(inst->alg.co.base.cra_blocksize))
 		goto out_free_inst;
 
+	if (inst->alg.co.statesize)
+		goto out_free_inst;
+
 	inst->alg.encrypt = crypto_cbc_encrypt;
 	inst->alg.decrypt = crypto_cbc_decrypt;
 
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt