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| author | Herbert Xu <herbert@gondor.apana.org.au> | 2020-04-10 16:09:42 +1000 |
|---|---|---|
| committer | Herbert Xu <herbert@gondor.apana.org.au> | 2020-04-16 16:49:22 +1000 |
| commit | 6603523bf5e432c7c8490fb500793bb15d4e5f61 (patch) | |
| tree | a55f489fb787cdc482819bcf29a1a0327549637e /crypto/algapi.c | |
| parent | eebac678556d6927f09a992872f4464cf3aecc76 (diff) | |
| download | lwn-6603523bf5e432c7c8490fb500793bb15d4e5f61.tar.gz lwn-6603523bf5e432c7c8490fb500793bb15d4e5f61.zip | |
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: 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>
Diffstat (limited to 'crypto/algapi.c')
| -rw-r--r-- | crypto/algapi.c | 22 |
1 files changed, 16 insertions, 6 deletions
diff --git a/crypto/algapi.c b/crypto/algapi.c index 849254d7e627..f1e6ccaff853 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, |