[PATCH 5.15] crypto: sun4i-ss - Remove insecure and unused rng_alg

[PATCH 5.15] crypto: sun4i-ss - Remove insecure and unused rng_alg

[Eric Biggers]

commit b2c41fa9dd8fc740c489e060b199165771f268d1 upstream.

Remove sun4i_ss_rng, as it is insecure and unused:

- It has multiple vulnerabilities.  sun4i_ss_prng_seed() is missing
  locking and has a buffer overflow.  sun4i_ss_prng_generate() fails to
  fill the entire buffer with cryptographic random bytes, because it
  rounds the destination length down and also doesn't actually wait for
  the hardware to be ready before pulling bytes from it.

- No user of this code is known.  It's usable only theoretically via the
  "rng" algorithm type of AF_ALG.  But userspace actually just uses the
  actual Linux RNG (/dev/random etc) instead.  And rng_algs don't
  contribute entropy to the actual Linux RNG either.  (This may have
  been confused with hwrng, which does contribute entropy.)

The sun4i_ss_prng_seed() buffer overflow was reported by Tianchu Chen
and discovered by Atuin - Automated Vulnerability Discovery Engine

There's no point in fixing all these vulnerabilities individually when
this is unused code, so let's just remove it.

Fixes: b8ae5c7387ad ("crypto: sun4i-ss - support the Security System PRNG")
Cc: stable@vger.kernel.org
Reported-by: Tianchu Chen <flynnnchen@tencent.com>
Closes: https://lore.kernel.org/r/af749a8447bd7f0e9dd26ca6c87e9c6afecb09d9@linux.dev/
Acked-by: Corentin LABBE <clabbe.montjoie@gmail.com>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---
 arch/arm/configs/sunxi_defconfig              |  1 -
 drivers/crypto/allwinner/Kconfig              |  8 ---
 drivers/crypto/allwinner/sun4i-ss/Makefile    |  1 -
 .../crypto/allwinner/sun4i-ss/sun4i-ss-core.c | 36 ----------
 .../crypto/allwinner/sun4i-ss/sun4i-ss-prng.c | 69 -------------------
 drivers/crypto/allwinner/sun4i-ss/sun4i-ss.h  | 20 ------
 6 files changed, 135 deletions(-)
 delete mode 100644 drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c

diff --git a/arch/arm/configs/sunxi_defconfig b/arch/arm/configs/sunxi_defconfig
index a60c134c5e04..5127c937b485 100644
--- a/arch/arm/configs/sunxi_defconfig
+++ b/arch/arm/configs/sunxi_defconfig
@@ -168,7 +168,6 @@ CONFIG_ROOT_NFS=y
 CONFIG_NLS_CODEPAGE_437=y
 CONFIG_NLS_ISO8859_1=y
 CONFIG_CRYPTO_DEV_SUN4I_SS=y
-CONFIG_CRYPTO_DEV_SUN4I_SS_PRNG=y
 CONFIG_CRYPTO_DEV_SUN8I_CE=y
 CONFIG_CRYPTO_DEV_SUN8I_SS=y
 CONFIG_DMA_CMA=y
diff --git a/drivers/crypto/allwinner/Kconfig b/drivers/crypto/allwinner/Kconfig
index b8e75210a0e3..06ea0e9fe6f2 100644
--- a/drivers/crypto/allwinner/Kconfig
+++ b/drivers/crypto/allwinner/Kconfig
@@ -24,14 +24,6 @@ config CRYPTO_DEV_SUN4I_SS
 	  To compile this driver as a module, choose M here: the module
 	  will be called sun4i-ss.
 
-config CRYPTO_DEV_SUN4I_SS_PRNG
-	bool "Support for Allwinner Security System PRNG"
-	depends on CRYPTO_DEV_SUN4I_SS
-	select CRYPTO_RNG
-	help
-	  Select this option if you want to provide kernel-side support for
-	  the Pseudo-Random Number Generator found in the Security System.
-
 config CRYPTO_DEV_SUN4I_SS_DEBUG
 	bool "Enable sun4i-ss stats"
 	depends on CRYPTO_DEV_SUN4I_SS
diff --git a/drivers/crypto/allwinner/sun4i-ss/Makefile b/drivers/crypto/allwinner/sun4i-ss/Makefile
index c0a2797d3168..06a9ae81f9f8 100644
--- a/drivers/crypto/allwinner/sun4i-ss/Makefile
+++ b/drivers/crypto/allwinner/sun4i-ss/Makefile
@@ -1,4 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_CRYPTO_DEV_SUN4I_SS) += sun4i-ss.o
 sun4i-ss-y += sun4i-ss-core.o sun4i-ss-hash.o sun4i-ss-cipher.o
-sun4i-ss-$(CONFIG_CRYPTO_DEV_SUN4I_SS_PRNG) += sun4i-ss-prng.o
diff --git a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c
index 44b8fc4b786d..0520cc6447e2 100644
--- a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c
+++ b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c
@@ -216,23 +216,6 @@ static struct sun4i_ss_alg_template ss_algs[] = {
 		}
 	}
 },
-#ifdef CONFIG_CRYPTO_DEV_SUN4I_SS_PRNG
-{
-	.type = CRYPTO_ALG_TYPE_RNG,
-	.alg.rng = {
-		.base = {
-			.cra_name		= "stdrng",
-			.cra_driver_name	= "sun4i_ss_rng",
-			.cra_priority		= 300,
-			.cra_ctxsize		= 0,
-			.cra_module		= THIS_MODULE,
-		},
-		.generate               = sun4i_ss_prng_generate,
-		.seed                   = sun4i_ss_prng_seed,
-		.seedsize               = SS_SEED_LEN / BITS_PER_BYTE,
-	}
-},
-#endif
 };
 
 static int sun4i_ss_dbgfs_read(struct seq_file *seq, void *v)
@@ -250,12 +233,6 @@ static int sun4i_ss_dbgfs_read(struct seq_file *seq, void *v)
 				   ss_algs[i].stat_req, ss_algs[i].stat_opti, ss_algs[i].stat_fb,
 				   ss_algs[i].stat_bytes);
 			break;
-		case CRYPTO_ALG_TYPE_RNG:
-			seq_printf(seq, "%s %s reqs=%lu tsize=%lu\n",
-				   ss_algs[i].alg.rng.base.cra_driver_name,
-				   ss_algs[i].alg.rng.base.cra_name,
-				   ss_algs[i].stat_req, ss_algs[i].stat_bytes);
-			break;
 		case CRYPTO_ALG_TYPE_AHASH:
 			seq_printf(seq, "%s %s reqs=%lu\n",
 				   ss_algs[i].alg.hash.halg.base.cra_driver_name,
@@ -486,13 +463,6 @@ static int sun4i_ss_probe(struct platform_device *pdev)
 				goto error_alg;
 			}
 			break;
-		case CRYPTO_ALG_TYPE_RNG:
-			err = crypto_register_rng(&ss_algs[i].alg.rng);
-			if (err) {
-				dev_err(ss->dev, "Fail to register %s\n",
-					ss_algs[i].alg.rng.base.cra_name);
-			}
-			break;
 		}
 	}
 
@@ -512,9 +482,6 @@ static int sun4i_ss_probe(struct platform_device *pdev)
 		case CRYPTO_ALG_TYPE_AHASH:
 			crypto_unregister_ahash(&ss_algs[i].alg.hash);
 			break;
-		case CRYPTO_ALG_TYPE_RNG:
-			crypto_unregister_rng(&ss_algs[i].alg.rng);
-			break;
 		}
 	}
 error_pm:
@@ -535,9 +502,6 @@ static int sun4i_ss_remove(struct platform_device *pdev)
 		case CRYPTO_ALG_TYPE_AHASH:
 			crypto_unregister_ahash(&ss_algs[i].alg.hash);
 			break;
-		case CRYPTO_ALG_TYPE_RNG:
-			crypto_unregister_rng(&ss_algs[i].alg.rng);
-			break;
 		}
 	}
 
diff --git a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c
deleted file mode 100644
index 491fcb7b81b4..000000000000
--- a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c
+++ /dev/null
@@ -1,69 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-#include "sun4i-ss.h"
-
-int sun4i_ss_prng_seed(struct crypto_rng *tfm, const u8 *seed,
-		       unsigned int slen)
-{
-	struct sun4i_ss_alg_template *algt;
-	struct rng_alg *alg = crypto_rng_alg(tfm);
-
-	algt = container_of(alg, struct sun4i_ss_alg_template, alg.rng);
-	memcpy(algt->ss->seed, seed, slen);
-
-	return 0;
-}
-
-int sun4i_ss_prng_generate(struct crypto_rng *tfm, const u8 *src,
-			   unsigned int slen, u8 *dst, unsigned int dlen)
-{
-	struct sun4i_ss_alg_template *algt;
-	struct rng_alg *alg = crypto_rng_alg(tfm);
-	int i, err;
-	u32 v;
-	u32 *data = (u32 *)dst;
-	const u32 mode = SS_OP_PRNG | SS_PRNG_CONTINUE | SS_ENABLED;
-	size_t len;
-	struct sun4i_ss_ctx *ss;
-	unsigned int todo = (dlen / 4) * 4;
-
-	algt = container_of(alg, struct sun4i_ss_alg_template, alg.rng);
-	ss = algt->ss;
-
-	err = pm_runtime_resume_and_get(ss->dev);
-	if (err < 0)
-		return err;
-
-	if (IS_ENABLED(CONFIG_CRYPTO_DEV_SUN4I_SS_DEBUG)) {
-		algt->stat_req++;
-		algt->stat_bytes += todo;
-	}
-
-	spin_lock_bh(&ss->slock);
-
-	writel(mode, ss->base + SS_CTL);
-
-	while (todo > 0) {
-		/* write the seed */
-		for (i = 0; i < SS_SEED_LEN / BITS_PER_LONG; i++)
-			writel(ss->seed[i], ss->base + SS_KEY0 + i * 4);
-
-		/* Read the random data */
-		len = min_t(size_t, SS_DATA_LEN / BITS_PER_BYTE, todo);
-		readsl(ss->base + SS_TXFIFO, data, len / 4);
-		data += len / 4;
-		todo -= len;
-
-		/* Update the seed */
-		for (i = 0; i < SS_SEED_LEN / BITS_PER_LONG; i++) {
-			v = readl(ss->base + SS_KEY0 + i * 4);
-			ss->seed[i] = v;
-		}
-	}
-
-	writel(0, ss->base + SS_CTL);
-	spin_unlock_bh(&ss->slock);
-
-	pm_runtime_put(ss->dev);
-
-	return 0;
-}
diff --git a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss.h b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss.h
index 0fee6f4e2d90..e1a849ce11b1 100644
--- a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss.h
+++ b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss.h
@@ -31,8 +31,6 @@
 #include <crypto/internal/skcipher.h>
 #include <crypto/aes.h>
 #include <crypto/internal/des.h>
-#include <crypto/internal/rng.h>
-#include <crypto/rng.h>
 
 #define SS_CTL            0x00
 #define SS_KEY0           0x04
@@ -62,10 +60,6 @@
 
 /* SS_CTL configuration values */
 
-/* PRNG generator mode - bit 15 */
-#define SS_PRNG_ONESHOT		(0 << 15)
-#define SS_PRNG_CONTINUE	(1 << 15)
-
 /* IV mode for hash */
 #define SS_IV_ARBITRARY		(1 << 14)
 
@@ -94,14 +88,10 @@
 #define SS_OP_3DES		(2 << 4)
 #define SS_OP_SHA1		(3 << 4)
 #define SS_OP_MD5		(4 << 4)
-#define SS_OP_PRNG		(5 << 4)
 
 /* Data end bit - bit 2 */
 #define SS_DATA_END		(1 << 2)
 
-/* PRNG start bit - bit 1 */
-#define SS_PRNG_START		(1 << 1)
-
 /* SS Enable bit - bit 0 */
 #define SS_DISABLED		(0 << 0)
 #define SS_ENABLED		(1 << 0)
@@ -128,9 +118,6 @@
 #define SS_RXFIFO_EMP_INT_ENABLE	(1 << 2)
 #define SS_TXFIFO_AVA_INT_ENABLE	(1 << 0)
 
-#define SS_SEED_LEN 192
-#define SS_DATA_LEN 160
-
 /*
  * struct ss_variant - Describe SS hardware variant
  * @sha1_in_be:		The SHA1 digest is given by SS in BE, and so need to be inverted.
@@ -151,9 +138,6 @@ struct sun4i_ss_ctx {
 	char buf[4 * SS_RX_MAX];/* buffer for linearize SG src */
 	char bufo[4 * SS_TX_MAX]; /* buffer for linearize SG dst */
 	spinlock_t slock; /* control the use of the device */
-#ifdef CONFIG_CRYPTO_DEV_SUN4I_SS_PRNG
-	u32 seed[SS_SEED_LEN / BITS_PER_LONG];
-#endif
 	struct dentry *dbgfs_dir;
 	struct dentry *dbgfs_stats;
 };
@@ -164,7 +148,6 @@ struct sun4i_ss_alg_template {
 	union {
 		struct skcipher_alg crypto;
 		struct ahash_alg hash;
-		struct rng_alg rng;
 	} alg;
 	struct sun4i_ss_ctx *ss;
 	unsigned long stat_req;
@@ -230,6 +213,3 @@ int sun4i_ss_des_setkey(struct crypto_skcipher *tfm, const u8 *key,
 			unsigned int keylen);
 int sun4i_ss_des3_setkey(struct crypto_skcipher *tfm, const u8 *key,
 			 unsigned int keylen);
-int sun4i_ss_prng_generate(struct crypto_rng *tfm, const u8 *src,
-			   unsigned int slen, u8 *dst, unsigned int dlen);
-int sun4i_ss_prng_seed(struct crypto_rng *tfm, const u8 *seed, unsigned int slen);

base-commit: c86c4726e7f044ab73b493c6f00527aafef640cd
-- 
2.55.0

Re: [PATCH 5.15] crypto: sun4i-ss - Remove insecure and unused rng_alg

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] The driver fails to remove its debugfs directory on device removal or module unload, leading to a dangling debugfs entry that can cause a use-after-free and kernel panic.
--

--- Patch [1]: [PATCH 5.15] crypto: sun4i-ss - Remove insecure and unused rng_alg ---
commit 170a30200701519fc546c370a0ab6113fdc3a608
Author: Eric Biggers <ebiggers@kernel.org>

crypto: sun4i-ss - Remove insecure and unused rng_alg

This commit removes the sun4i_ss_rng implementation because it is insecure,
has multiple vulnerabilities including a buffer overflow, and is unused.
There is no point in fixing these issues individually when the code is
unneeded.

Closes: https://lore.kernel.org/r/af749a8447bd7f0e9dd26ca6c87e9c6afecb09d9@linux.dev/

> diff --git a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c
> --- a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c
> +++ b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-core.c

[ ... ]

> @@ -535,9 +502,6 @@ static int sun4i_ss_remove(struct platform_device *pdev)
>  		case CRYPTO_ALG_TYPE_AHASH:
>  			crypto_unregister_ahash(&ss_algs[i].alg.hash);
>  			break;
> -		case CRYPTO_ALG_TYPE_RNG:
> -			crypto_unregister_rng(&ss_algs[i].alg.rng);
> -			break;
>  		}
>  	}
>  

[Severity: High]
This is a pre-existing issue, but does this function leak the debugfs
directory when the module is removed?

In sun4i_ss_probe(), the driver sets up the debugfs entries:

    ss->dbgfs_dir = debugfs_create_dir("sun4i-ss", NULL);
    ss->dbgfs_stats = debugfs_create_file("stats", 0444, ss->dbgfs_dir, ss,
                                          &sun4i_ss_debugfs_fops);

Since sun4i_ss_remove() lacks a corresponding debugfs_remove_recursive()
call, could unloading the module leave the debugfs entries registered in the
VFS, leading to a use-after-free and kernel panic if someone opens
/sys/kernel/debug/sun4i-ss/stats after the module memory is freed?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260717035228.353051-1-ebiggers@kernel.org?part=1