| Message ID | 1542880816-63838-1-git-send-email-bianpan2016@163.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | crypto: do not free algorithm before using | expand |
On Thu, Nov 22, 2018 at 06:00:16PM +0800, Pan Bian wrote: > In multiple functions, the algorithm fields are read after its reference > is dropped through crypto_mod_put. In this case, the algorithm memory > may be freed, resulting in use-after-free bugs. This patch delays the > put operation until the algorithm is never used. > > Signed-off-by: Pan Bian <bianpan2016@163.com> I don't think this patch is needed. > --- > crypto/cbc.c | 6 ++++-- > crypto/cfb.c | 6 ++++-- > crypto/pcbc.c | 6 ++++-- > 3 files changed, 12 insertions(+), 6 deletions(-) > > diff --git a/crypto/cbc.c b/crypto/cbc.c > index b761b1f..dd5f332 100644 > --- a/crypto/cbc.c > +++ b/crypto/cbc.c > @@ -140,9 +140,8 @@ static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb) > spawn = skcipher_instance_ctx(inst); > err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst), > CRYPTO_ALG_TYPE_MASK); > - crypto_mod_put(alg); > if (err) > - goto err_free_inst; > + goto err_put_alg; We can safely drop the reference to the algorithm because the spawn is now meant to hold a reference to it. As long as the spawn is alive so will the algorithm. Cheers,
On Thu, Nov 22, 2018 at 10:44:41PM +0800, Herbert Xu wrote: > On Thu, Nov 22, 2018 at 06:00:16PM +0800, Pan Bian wrote: > > In multiple functions, the algorithm fields are read after its reference > > is dropped through crypto_mod_put. In this case, the algorithm memory > > may be freed, resulting in use-after-free bugs. This patch delays the > > put operation until the algorithm is never used. > > > > Signed-off-by: Pan Bian <bianpan2016@163.com> > > I don't think this patch is needed. > > > --- > > crypto/cbc.c | 6 ++++-- > > crypto/cfb.c | 6 ++++-- > > crypto/pcbc.c | 6 ++++-- > > 3 files changed, 12 insertions(+), 6 deletions(-) > > > > diff --git a/crypto/cbc.c b/crypto/cbc.c > > index b761b1f..dd5f332 100644 > > --- a/crypto/cbc.c > > +++ b/crypto/cbc.c > > @@ -140,9 +140,8 @@ static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb) > > spawn = skcipher_instance_ctx(inst); > > err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst), > > CRYPTO_ALG_TYPE_MASK); > > - crypto_mod_put(alg); > > if (err) > > - goto err_free_inst; > > + goto err_put_alg; > > We can safely drop the reference to the algorithm because the spawn > is now meant to hold a reference to it. As long as the spawn is > alive so will the algorithm. Thanks for your explanation! But I find that the function crypto_init_spawn just lets spawn->alg point to the algorithm without increasing the reference count, i.e., alg->cra_refcnt. So I am confused about how this can protect the algorithm from being freed. Maybe I missed some key points. Could you please explain it in more details? Thank you! Best regards, Pan Bian > > Cheers, > -- > Email: Herbert Xu <herbert@gondor.apana.org.au> > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
On Fri, Nov 23, 2018 at 09:05:55AM +0800, PanBian wrote: > > Thanks for your explanation! But I find that the function > crypto_init_spawn just lets spawn->alg point to the algorithm without > increasing the reference count, i.e., alg->cra_refcnt. So I am confused > about how this can protect the algorithm from being freed. Maybe I > missed some key points. Could you please explain it in more details? Oh you're right! This bug was introduced during the skcipher conversion. The spawns are not meant to carry a reference count with them because they are not supposed to stop the underlying algorithm from being removed. So yes we do need to hold a reference count on alg until the instance is registered. Thanks,
On Thu, Nov 22, 2018 at 06:00:16PM +0800, Pan Bian wrote: > In multiple functions, the algorithm fields are read after its reference > is dropped through crypto_mod_put. In this case, the algorithm memory > may be freed, resulting in use-after-free bugs. This patch delays the > put operation until the algorithm is never used. > > Signed-off-by: Pan Bian <bianpan2016@163.com> Patch applied. Thanks! BTW, this problem exists in almost every other skcipher template, e.g., in ctr. Are you working on a fix for them too? Cheers,
On Thu, Nov 29, 2018 at 02:57:11PM +0800, Herbert Xu wrote: > On Thu, Nov 22, 2018 at 06:00:16PM +0800, Pan Bian wrote: > > In multiple functions, the algorithm fields are read after its reference > > is dropped through crypto_mod_put. In this case, the algorithm memory > > may be freed, resulting in use-after-free bugs. This patch delays the > > put operation until the algorithm is never used. > > > > Signed-off-by: Pan Bian <bianpan2016@163.com> > > Patch applied. Thanks! > > BTW, this problem exists in almost every other skcipher template, > e.g., in ctr. Are you working on a fix for them too? Probably not. Could you please provide patches to fix them? Thanks, Pan > > Cheers, > -- > Email: Herbert Xu <herbert@gondor.apana.org.au> > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
On Thu, Nov 29, 2018 at 03:47:56PM +0800, PanBian wrote: > On Thu, Nov 29, 2018 at 02:57:11PM +0800, Herbert Xu wrote: > > On Thu, Nov 22, 2018 at 06:00:16PM +0800, Pan Bian wrote: > > > In multiple functions, the algorithm fields are read after its reference > > > is dropped through crypto_mod_put. In this case, the algorithm memory > > > may be freed, resulting in use-after-free bugs. This patch delays the > > > put operation until the algorithm is never used. > > > > > > Signed-off-by: Pan Bian <bianpan2016@163.com> > > > > Patch applied. Thanks! > > > > BTW, this problem exists in almost every other skcipher template, > > e.g., in ctr. Are you working on a fix for them too? > > Probably not. Could you please provide patches to fix them? OK, I'll work on it then. Thanks!
diff --git a/crypto/cbc.c b/crypto/cbc.c index b761b1f..dd5f332 100644 --- a/crypto/cbc.c +++ b/crypto/cbc.c @@ -140,9 +140,8 @@ static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb) spawn = skcipher_instance_ctx(inst); err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst), CRYPTO_ALG_TYPE_MASK); - crypto_mod_put(alg); if (err) - goto err_free_inst; + goto err_put_alg; err = crypto_inst_setname(skcipher_crypto_instance(inst), "cbc", alg); if (err) @@ -174,12 +173,15 @@ static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb) err = skcipher_register_instance(tmpl, inst); if (err) goto err_drop_spawn; + crypto_mod_put(alg); out: return err; err_drop_spawn: crypto_drop_spawn(spawn); +err_put_alg: + crypto_mod_put(alg); err_free_inst: kfree(inst); goto out; diff --git a/crypto/cfb.c b/crypto/cfb.c index a0d68c0..20987d0 100644 --- a/crypto/cfb.c +++ b/crypto/cfb.c @@ -286,9 +286,8 @@ static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb) spawn = skcipher_instance_ctx(inst); err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst), CRYPTO_ALG_TYPE_MASK); - crypto_mod_put(alg); if (err) - goto err_free_inst; + goto err_put_alg; err = crypto_inst_setname(skcipher_crypto_instance(inst), "cfb", alg); if (err) @@ -317,12 +316,15 @@ static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb) err = skcipher_register_instance(tmpl, inst); if (err) goto err_drop_spawn; + crypto_mod_put(alg); out: return err; err_drop_spawn: crypto_drop_spawn(spawn); +err_put_alg: + crypto_mod_put(alg); err_free_inst: kfree(inst); goto out; diff --git a/crypto/pcbc.c b/crypto/pcbc.c index ef802f6..8aa1014 100644 --- a/crypto/pcbc.c +++ b/crypto/pcbc.c @@ -244,9 +244,8 @@ static int crypto_pcbc_create(struct crypto_template *tmpl, struct rtattr **tb) spawn = skcipher_instance_ctx(inst); err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst), CRYPTO_ALG_TYPE_MASK); - crypto_mod_put(alg); if (err) - goto err_free_inst; + goto err_put_alg; err = crypto_inst_setname(skcipher_crypto_instance(inst), "pcbc", alg); if (err) @@ -275,12 +274,15 @@ static int crypto_pcbc_create(struct crypto_template *tmpl, struct rtattr **tb) err = skcipher_register_instance(tmpl, inst); if (err) goto err_drop_spawn; + crypto_mod_put(alg); out: return err; err_drop_spawn: crypto_drop_spawn(spawn); +err_put_alg: + crypto_mod_put(alg); err_free_inst: kfree(inst); goto out;
In multiple functions, the algorithm fields are read after its reference is dropped through crypto_mod_put. In this case, the algorithm memory may be freed, resulting in use-after-free bugs. This patch delays the put operation until the algorithm is never used. Signed-off-by: Pan Bian <bianpan2016@163.com> --- crypto/cbc.c | 6 ++++-- crypto/cfb.c | 6 ++++-- crypto/pcbc.c | 6 ++++-- 3 files changed, 12 insertions(+), 6 deletions(-)