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

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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: syzbot+fc0674cde00b66844470@syzkaller.appspotmail.com
Fixes: 4f87ee118d ("crypto: api - Do not zap spawn->alg")
Fixes: 73669cc556 ("crypto: api - Fix race condition in...")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Herbert Xu 2020-04-10 16:09:42 +10:00
parent eebac67855
commit 6603523bf5
3 changed files with 19 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
crypto/algapi.c
View File

@ -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);
alg = spawn->alg;
if (!spawn->dead && !crypto_mod_get(alg)) {
alg->cra_flags |= CRYPTO_ALG_DYING;
alg = NULL;
if (!spawn->dead) {
alg = spawn->alg;
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,

3
crypto/api.c
View File

@ -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)

1
crypto/internal.h
View File

@ -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,