| Message ID | 20200410060942.GA4048@gondor.apana.org.au |
|---|---|
| State | Accepted |
| Commit | 6603523bf5e432c7c8490fb500793bb15d4e5f61 |
| Headers | show |
| Series |
|
| Related | show |
On Fri, Apr 10, 2020 at 04:09:42PM +1000, Herbert Xu wrote: > 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: 4f87ee118d16 ("crypto: api - Do not zap spawn->alg") > Fixes: 73669cc55646 ("crypto: api - Fix race condition in...") > Cc: <stable@vger.kernel.org> > Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> > > diff --git a/crypto/algapi.c b/crypto/algapi.c > index 69605e21af92..f8b4dc161c02 100644 > --- a/crypto/algapi.c > +++ b/crypto/algapi.c > @@ -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; > } Wouldn't it be a bit simpler to set 'target = NULL', remove 'shoot', and use 'if (target)' instead of 'if (shoot)'? - Eric
On Wed, Apr 15, 2020 at 07:17:03PM -0700, Eric Biggers wrote: > > Wouldn't it be a bit simpler to set 'target = NULL', remove 'shoot', > and use 'if (target)' instead of 'if (shoot)'? Yes it is simpler but it's actually semantically different because the compiler doesn't know that spawn->alg cannot be NULL in this case. Thanks,
On Thu, Apr 16, 2020 at 12:25:02PM +1000, Herbert Xu wrote: > On Wed, Apr 15, 2020 at 07:17:03PM -0700, Eric Biggers wrote: > > > > Wouldn't it be a bit simpler to set 'target = NULL', remove 'shoot', > > and use 'if (target)' instead of 'if (shoot)'? > > Yes it is simpler but it's actually semantically different because > the compiler doesn't know that spawn->alg cannot be NULL in this > case. > I'm not sure what you mean here. crypto_alg_get() is: static inline struct crypto_alg *crypto_alg_get(struct crypto_alg *alg) { refcount_inc(&alg->cra_refcnt); return alg; } So given: target = crypto_alg_get(alg); Both alg and target have to be non-NULL. - Eric
On Wed, Apr 15, 2020 at 07:30:01PM -0700, Eric Biggers wrote: > > I'm not sure what you mean here. crypto_alg_get() is: > > static inline struct crypto_alg *crypto_alg_get(struct crypto_alg *alg) > { > refcount_inc(&alg->cra_refcnt); > return alg; > } > > So given: > > target = crypto_alg_get(alg); > > Both alg and target have to be non-NULL. Yes I know that we know that it can't be NULL, but gcc 8.3 doesn't. Cheers,
diff --git a/crypto/algapi.c b/crypto/algapi.c index 69605e21af92..f8b4dc161c02 100644 --- a/crypto/algapi.c +++ b/crypto/algapi.c @@ -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, diff --git a/crypto/api.c b/crypto/api.c index 7d71a9b10e5f..edcf690800d4 100644 --- a/crypto/api.c +++ b/crypto/api.c @@ -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) diff --git a/crypto/internal.h b/crypto/internal.h index d5ebc60c5143..ff06a3bd1ca1 100644 --- a/crypto/internal.h +++ b/crypto/internal.h @@ -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,
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: 4f87ee118d16 ("crypto: api - Do not zap spawn->alg") Fixes: 73669cc55646 ("crypto: api - Fix race condition in...") Cc: <stable@vger.kernel.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>