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| author | Eric Biggers <ebiggers@google.com> | 2017-12-29 23:30:19 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-01-17 11:45:23 +0300 |
| commit | 3662493dbdad17c3d144cfb73d0c897ccc28cc52 (patch) | |
| tree | f7d0bc1e938ae32840e1ae696c1f313b14fc4869 /crypto | |
| parent | d01c7936966982fa6723ec80c018c5e89045fde3 (diff) | |
| download | linux-3662493dbdad17c3d144cfb73d0c897ccc28cc52.tar.xz | |
crypto: algapi - fix NULL dereference in crypto_remove_spawns()
commit 9a00674213a3f00394f4e3221b88f2d21fc05789 upstream.
syzkaller triggered a NULL pointer dereference in crypto_remove_spawns()
via a program that repeatedly and concurrently requests AEADs
"authenc(cmac(des3_ede-asm),pcbc-aes-aesni)" and hashes "cmac(des3_ede)"
through AF_ALG, where the hashes are requested as "untested"
(CRYPTO_ALG_TESTED is set in ->salg_mask but clear in ->salg_feat; this
causes the template to be instantiated for every request).
Although AF_ALG users really shouldn't be able to request an "untested"
algorithm, the NULL pointer dereference is actually caused by a
longstanding race condition where crypto_remove_spawns() can encounter
an instance which has had spawn(s) "grabbed" but hasn't yet been
registered, resulting in ->cra_users still being NULL.
We probably should properly initialize ->cra_users earlier, but that
would require updating many templates individually. For now just fix
the bug in a simple way that can easily be backported: make
crypto_remove_spawns() treat a NULL ->cra_users list as empty.
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'crypto')
| -rw-r--r-- | crypto/algapi.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/crypto/algapi.c b/crypto/algapi.c index aa699ff6c876..50eb828db767 100644 --- a/crypto/algapi.c +++ b/crypto/algapi.c @@ -167,6 +167,18 @@ void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list, spawn->alg = NULL; spawns = &inst->alg.cra_users; + + /* + * We may encounter an unregistered instance here, since + * an instance's spawns are set up prior to the instance + * being registered. An unregistered instance will have + * NULL ->cra_users.next, since ->cra_users isn't + * properly initialized until registration. But an + * unregistered instance cannot have any users, so treat + * it the same as ->cra_users being empty. + */ + if (spawns->next == NULL) + break; } } while ((spawns = crypto_more_spawns(alg, &stack, &top, &secondary_spawns))); |