From: Lukas Wunner <lukas@wunner.de>
To: Thorsten Blum <thorsten.blum@linux.dev>
Cc: David Howells <dhowells@redhat.com>,
Ignat Korchagin <ignat@cloudflare.com>,
Herbert Xu <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
Vivek Goyal <vgoyal@redhat.com>,
stable@vger.kernel.org, keyrings@vger.kernel.org,
linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] crypto: asymmetric_keys - prevent overflow in asymmetric_key_generate_id
Date: Mon, 13 Oct 2025 10:31:25 +0200 [thread overview]
Message-ID: <aOy43TmVgWvzNGfB@wunner.de> (raw)
In-Reply-To: <4AF8BE0F-D400-4020-A8F6-EF61A797A24E@linux.dev>
On Mon, Oct 13, 2025 at 10:23:01AM +0200, Thorsten Blum wrote:
> On 13. Oct 2025, at 08:24, Lukas Wunner wrote:
> > On Sun, Oct 12, 2025 at 10:38:40PM +0200, Thorsten Blum wrote:
> >> +++ b/crypto/asymmetric_keys/asymmetric_type.c
> >> @@ -141,12 +142,14 @@ struct asymmetric_key_id *asymmetric_key_generate_id(const void *val_1,
> >> size_t len_2)
> >> {
> >> struct asymmetric_key_id *kid;
> >> + size_t len;
> >>
> >> - kid = kmalloc(sizeof(struct asymmetric_key_id) + len_1 + len_2,
> >> - GFP_KERNEL);
> >> + if (check_add_overflow(len_1, len_2, &len))
> >> + return ERR_PTR(-EOVERFLOW);
> >> + kid = kmalloc(struct_size(kid, data, len), GFP_KERNEL);
> >
> > This will add (at least) 2 bytes to len (namely the size of struct
> > asymmetric_key_id)) and may cause an overflow (even if len_1 + len_2
> > did not overflow).
>
> Could you explain which part adds "(at least) 2 bytes to len"?
The struct_size() macro performs another size_add() to add the
size of struct asymmetric_key_id (which is at least 2 bytes) to len:
#define struct_size(p, member, count) \
__builtin_choose_expr(__is_constexpr(count), \
sizeof(*(p)) + flex_array_size(p, member, count), \
size_add(sizeof(*(p)), flex_array_size(p, member, count)))
^^^^^^^^
So there's an addition of three numbers, yet you're only checking that
the addition of two of them doesn't overflow.
Thanks,
Lukas
prev parent reply other threads:[~2025-10-13 8:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-12 20:38 [PATCH v2 1/2] crypto: asymmetric_keys - prevent overflow in asymmetric_key_generate_id Thorsten Blum
2025-10-12 20:38 ` [PATCH v2 2/2] crypto: asymmetric_keys - simplify asymmetric_key_hex_to_key_id Thorsten Blum
2025-10-13 6:24 ` [PATCH v2 1/2] crypto: asymmetric_keys - prevent overflow in asymmetric_key_generate_id Lukas Wunner
2025-10-13 8:23 ` Thorsten Blum
2025-10-13 8:31 ` Lukas Wunner [this message]
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