[PATCH] crypto: aes - Fix conditions for selecting MAC dependencies

[PATCH] crypto: aes - Fix conditions for selecting MAC dependencies

[Eric Biggers]

Starting in commit 7137cbf2b5c9 ("crypto: aes - Add cmac, xcbc, and
cbcmac algorithms using library"), the aes module (CRYPTO_AES) supports
CBC based MACs using the corresponding library functions.

To avoid including unneeded functionality, that support honors the
existing CRYPTO_CMAC, CRYPTO_XCBC, and CRYPTO_CCM kconfig options.  The
dependencies are selected if at least one of those is enabled.

However, the select statements don't correctly handle the case where
CRYPTO_AES=y and (for example) CRYPTO_CMAC=m.  In that case the
dependencies get selected at level 'm', due to how the kconfig language
works.  That causes a linker error.

Fix this by changing the selection conditions to use '!= n'.

A similar issue also exists for CRYPTO_LIB_AES's conditional selection
of CRYPTO_LIB_UTILS.  The same '!= n' would work, but instead just make
CRYPTO_LIB_AES always select CRYPTO_LIB_UTILS.  CRYPTO_LIB_UTILS is
lightweight, and it's needed by most AES modes and many other things.

Fixes: 7137cbf2b5c9 ("crypto: aes - Add cmac, xcbc, and cbcmac algorithms using library")
Fixes: 309a7e514da7 ("lib/crypto: aes: Add support for CBC-based MACs")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---

I'm planning to take this patch through libcrypto-fixes.

 crypto/Kconfig     | 4 ++--
 lib/crypto/Kconfig | 3 +--
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/crypto/Kconfig b/crypto/Kconfig
index f1e372195273..b61401bd3ef6 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -358,8 +358,8 @@ config CRYPTO_AES
 	tristate "AES (Advanced Encryption Standard)"
 	select CRYPTO_ALGAPI
 	select CRYPTO_LIB_AES
-	select CRYPTO_LIB_AES_CBC_MACS if CRYPTO_CMAC || CRYPTO_XCBC || CRYPTO_CCM
-	select CRYPTO_HASH if CRYPTO_CMAC || CRYPTO_XCBC || CRYPTO_CCM
+	select CRYPTO_LIB_AES_CBC_MACS if CRYPTO_CMAC != n || CRYPTO_XCBC != n || CRYPTO_CCM != n
+	select CRYPTO_HASH if CRYPTO_CMAC != n || CRYPTO_XCBC != n || CRYPTO_CCM != n
 	help
 	  AES cipher algorithms (Rijndael)(FIPS-197, ISO/IEC 18033-3)
 
diff --git a/lib/crypto/Kconfig b/lib/crypto/Kconfig
index 591c1c2a7fb3..83d4c95e079e 100644
--- a/lib/crypto/Kconfig
+++ b/lib/crypto/Kconfig
@@ -8,8 +8,7 @@ config CRYPTO_LIB_UTILS
 
 config CRYPTO_LIB_AES
 	tristate
-	# Select dependencies of modes that are part of libaes.
-	select CRYPTO_LIB_UTILS if CRYPTO_LIB_AES_CBC_MACS
+	select CRYPTO_LIB_UTILS
 
 config CRYPTO_LIB_AES_ARCH
 	bool

base-commit: 8cdeaa50eae8dad34885515f62559ee83e7e8dda
-- 
2.55.0

Re: [PATCH] crypto: aes - Fix conditions for selecting MAC dependencies

[Eric Biggers]

On Wed, Jul 08, 2026 at 10:29:54PM -0400, Eric Biggers wrote:
> Starting in commit 7137cbf2b5c9 ("crypto: aes - Add cmac, xcbc, and
> cbcmac algorithms using library"), the aes module (CRYPTO_AES) supports
> CBC based MACs using the corresponding library functions.
> 
> To avoid including unneeded functionality, that support honors the
> existing CRYPTO_CMAC, CRYPTO_XCBC, and CRYPTO_CCM kconfig options.  The
> dependencies are selected if at least one of those is enabled.
> 
> However, the select statements don't correctly handle the case where
> CRYPTO_AES=y and (for example) CRYPTO_CMAC=m.  In that case the
> dependencies get selected at level 'm', due to how the kconfig language
> works.  That causes a linker error.
> 
> Fix this by changing the selection conditions to use '!= n'.
> 
> A similar issue also exists for CRYPTO_LIB_AES's conditional selection
> of CRYPTO_LIB_UTILS.  The same '!= n' would work, but instead just make
> CRYPTO_LIB_AES always select CRYPTO_LIB_UTILS.  CRYPTO_LIB_UTILS is
> lightweight, and it's needed by most AES modes and many other things.
> 
> Fixes: 7137cbf2b5c9 ("crypto: aes - Add cmac, xcbc, and cbcmac algorithms using library")
> Fixes: 309a7e514da7 ("lib/crypto: aes: Add support for CBC-based MACs")
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
> ---
> 

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=libcrypto-fixes

- Eric