2020-08-02 18:02:55

by Tom Rix

Subject: [PATCH] crypto: drbg: check blocklen is non zero

From: Tom Rix <[email protected]>

Clang static analysis reports this error

crypto/drbg.c:441:40: warning: Division by zero
padlen = (inputlen + sizeof(L_N) + 1) % (drbg_blocklen(drbg));
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

When drbg_bocklen fails it returns 0.

if (drbg && drbg->core)
return drbg->core->blocklen_bytes;
return 0;

In many places in drbg_ctr_df drbg_bocklen is assumed to be non zero.
So turn the assumption into a check.

Fixes: 541af946fe13 ("crypto: drbg - SP800-90A Deterministic Random Bit Generator")

Signed-off-by: Tom Rix <[email protected]>
---
crypto/drbg.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/crypto/drbg.c b/crypto/drbg.c
index e99fe34cfa00..bd9a137e5473 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -420,6 +420,9 @@ static int drbg_ctr_df(struct drbg_state *drbg,
size_t inputlen = 0;
struct drbg_string *seed = NULL;

+ if (!drbg_blocklen(drbg))
+ return -EINVAL;
+
memset(pad, 0, drbg_blocklen(drbg));
memset(iv, 0, drbg_blocklen(drbg));

--
2.18.1

2020-08-02 18:29:41

by Stephan Müller

Subject: Re: [PATCH] crypto: drbg: check blocklen is non zero

Am Sonntag, 2. August 2020, 19:12:47 CEST schrieb [email protected]:

Hi Tom,

> From: Tom Rix <[email protected]>
>
> Clang static analysis reports this error
>
> crypto/drbg.c:441:40: warning: Division by zero
> padlen = (inputlen + sizeof(L_N) + 1) % (drbg_blocklen(drbg));
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
>
> When drbg_bocklen fails it returns 0.
>
> if (drbg && drbg->core)
> return drbg->core->blocklen_bytes;
> return 0;
>
> In many places in drbg_ctr_df drbg_bocklen is assumed to be non zero.
> So turn the assumption into a check.
>
> Fixes: 541af946fe13 ("crypto: drbg - SP800-90A Deterministic Random Bit
> Generator")
>
> Signed-off-by: Tom Rix <[email protected]>

Thank you.

Reviewed-by: Stephan Mueller <[email protected]>

Ciao
Stephan