Commit 6603523b authored by Herbert Xu's avatar Herbert Xu
Browse files

crypto: api - Fix use-after-free and race in crypto_spawn_alg 



There are two problems in crypto_spawn_alg.  First of all it may
return spawn->alg even if spawn->dead is set.  This results in a
double-free as detected by syzbot.

Secondly the setting of the DYING flag is racy because we hold
the read-lock instead of the write-lock.  We should instead call
crypto_shoot_alg in a safe manner by gaining a refcount, dropping
the lock, and then releasing the refcount.

This patch fixes both problems.

Reported-by: default avatar <syzbot+fc0674cde00b66844470@syzkaller.appspotmail.com>
Fixes: 4f87ee11 ("crypto: api - Do not zap spawn->alg")
Fixes: 73669cc5 ("crypto: api - Fix race condition in...")
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent eebac678

crypto/algapi.c

+16 −6
Original line number Diff line number Diff line
@@ -716,17 +716,27 @@ EXPORT_SYMBOL_GPL(crypto_drop_spawn); 


static struct crypto_alg *crypto_spawn_alg(struct crypto_spawn *spawn)

{

	struct crypto_alg *alg;

	struct crypto_alg *alg = ERR_PTR(-EAGAIN);

	struct crypto_alg *target;

	bool shoot = false;



	down_read(&crypto_alg_sem);

	if (!spawn->dead) {

		alg = spawn->alg;

	if (!spawn->dead && !crypto_mod_get(alg)) {

		alg->cra_flags |= CRYPTO_ALG_DYING;

		alg = NULL;

		if (!crypto_mod_get(alg)) {

			target = crypto_alg_get(alg);

			shoot = true;

			alg = ERR_PTR(-EAGAIN);

		}

	}

	up_read(&crypto_alg_sem);



	return alg ?: ERR_PTR(-EAGAIN);

	if (shoot) {

		crypto_shoot_alg(target);

		crypto_alg_put(target);

	}



	return alg;

}



struct crypto_tfm *crypto_spawn_tfm(struct crypto_spawn *spawn, u32 type,

crypto/api.c

+2 −1
Original line number Diff line number Diff line
@@ -333,12 +333,13 @@ static unsigned int crypto_ctxsize(struct crypto_alg *alg, u32 type, u32 mask) 
	return len;

}



static void crypto_shoot_alg(struct crypto_alg *alg)

void crypto_shoot_alg(struct crypto_alg *alg)

{

	down_write(&crypto_alg_sem);

	alg->cra_flags |= CRYPTO_ALG_DYING;

	up_write(&crypto_alg_sem);

}

EXPORT_SYMBOL_GPL(crypto_shoot_alg);



struct crypto_tfm *__crypto_alloc_tfm(struct crypto_alg *alg, u32 type,

				      u32 mask)

crypto/internal.h

+1 −0
Original line number Diff line number Diff line
@@ -65,6 +65,7 @@ void crypto_alg_tested(const char *name, int err); 
void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,

			  struct crypto_alg *nalg);

void crypto_remove_final(struct list_head *list);

void crypto_shoot_alg(struct crypto_alg *alg);

struct crypto_tfm *__crypto_alloc_tfm(struct crypto_alg *alg, u32 type,

				      u32 mask);

void *crypto_create_tfm(struct crypto_alg *alg,

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