Crash when using ahash_request_ctx

Hello

I have a problem when using a simple md5 tfm.
When I use the data that ahash_request_ctx() give me, it will cause random crash when removing the module later. I do not understand it, because .cra_ctxsize seems to be rightly used.

The very simplified POC code will follow, it register a fake md5 implementation.
If I remove the op->mode = 0, I can modprobe/rmmod for ever without problem.
With it, rmmod will segfault in 2 or 3 tries, so it is this write that is the source of the problem.

I have try to debug, but I cannot find where __ctx (the pointer returned by ahash_request_ctx) is allocated.

Does I am right when saying: ahash_request_ctx() return the pointer to a structure of size equal to cra_ctxsize allocated for each request ?

Thanks in advance

Best regards

#include <linux/clk.h>
#include <linux/crypto.h>
#include <linux/io.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <crypto/scatterwalk.h>
#include <linux/scatterlist.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <crypto/md5.h>
#include <crypto/sha.h>
#include <crypto/hash.h>
#include <crypto/internal/hash.h>

struct sunxi_req_ctx {
	u8 key[32 * 8];
	u32 keylen;
	u32 mode;
	u64 byte_count;
	u32 waitbuf;
	unsigned int nbwait;
};

int fake_init(struct ahash_request *areq) {
	struct sunxi_req_ctx *op = ahash_request_ctx(areq);
	/* this is the location of action that cause the crash */
	op->mode = 0;
	op->nbwait = 0;
	return 0;
}
int fake_update(struct ahash_request *areq) {
	return 0;
}
int fake_final(struct ahash_request *areq) {
	return 0;
}
int fake_finup(struct ahash_request *areq) {
	fake_init(areq);
	return 0;
}
int fake_digest(struct ahash_request *areq) {
	fake_init(areq);
	return 0;
}

static struct ahash_alg sunxi_md5_alg = {
.init = fake_init,
.update = fake_update,
.final = fake_final,
.finup = fake_finup,
.digest = fake_digest,
.halg = {
.digestsize = MD5_DIGEST_SIZE,
.base = {
.cra_name = "md5",
.cra_driver_name = "md5-sunxi-ss", .cra_priority = 300,
.cra_alignmask = 3,
.cra_flags = CRYPTO_ALG_TYPE_AHASH | CRYPTO_ALG_ASYNC, .cra_blocksize = MD5_HMAC_BLOCK_SIZE, .cra_ctxsize = sizeof(struct sunxi_req_ctx), .cra_module = THIS_MODULE,
.cra_type = &crypto_ahash_type
}
}
};

static int sunxi_ss_md5_init(void)

{
	int err = 0;
	err = crypto_register_ahash(&sunxi_md5_alg);
	if (err)
		pr_err("crypto_register_alg error for MD5\n");
	else
		pr_info("Registred MD5\n");
	return err;
}

static void __exit sunxi_ss_md5_exit(void)

{
	crypto_unregister_ahash(&sunxi_md5_alg);
}

module_init(sunxi_ss_md5_init);
module_exit(sunxi_ss_md5_exit);

MODULE_DESCRIPTION("test MD5 module"); MODULE_LICENSE("GPL");
MODULE_AUTHOR("Corentin LABBE <[email protected]>");

crypto_tfm_ctx() returns per-transformation instance (tfm) private data ahash_request_ctx() returns per-request private data

You need to configure the request context size via crypto_ahash_set_reqsize() in the implementations' .cra_init() callback .

[...]

static int my_cra_init(struct crypto_tfm *tfm) {
crypto_ahash_set_reqsize(__crypto_ahash_cast(tfm),

                          sizeof(struct my_per_request_private_data));

return 0;
}

.cra_init = my_cra_init,

module_platform_driver() here please, fix it up so this is a platform driver.