From e7a4142b35ce489fc8908d75596c51549711ade0 Mon Sep 17 00:00:00 2001 From: Herbert Xu Date: Sun, 1 Sep 2024 16:05:40 +0800 Subject: [PATCH] crypto: api - Fix generic algorithm self-test races On Fri, Aug 30, 2024 at 10:51:54AM -0700, Eric Biggers wrote: > > Given below in defconfig form, use 'make olddefconfig' to apply. The failures > are nondeterministic and sometimes there are different ones, for example: > > [ 0.358017] alg: skcipher: failed to allocate transform for cbc(twofish-generic): -2 > [ 0.358365] alg: self-tests for cbc(twofish) using cbc(twofish-generic) failed (rc=-2) > [ 0.358535] alg: skcipher: failed to allocate transform for cbc(camellia-generic): -2 > [ 0.358918] alg: self-tests for cbc(camellia) using cbc(camellia-generic) failed (rc=-2) > [ 0.371533] alg: skcipher: failed to allocate transform for xts(ecb(aes-generic)): -2 > [ 0.371922] alg: self-tests for xts(aes) using xts(ecb(aes-generic)) failed (rc=-2) > > Modules are not enabled, maybe that matters (I haven't checked yet). Yes I think that was the key. This triggers a massive self-test run which executes in parallel and reveals a few race conditions in the system. I think it boils down to the following scenario: Base algorithm X-generic, X-optimised Template Y Optimised algorithm Y-X-optimised Everything gets registered, and then the self-tests are started. When Y-X-optimised gets tested, it requests the creation of the generic Y(X-generic). Which then itself undergoes testing. The race is that after Y(X-generic) gets registered, but just before it gets tested, X-optimised finally finishes self-testing which then causes all spawns of X-generic to be destroyed. So by the time the self-test for Y(X-generic) comes along, it can no longer find the algorithm. This error then bubbles up all the way up to the self-test of Y-X-optimised which then fails. Note that there is some complexity that I've omitted here because when the generic self-test fails to find Y(X-generic) it actually triggers the construction of it again which then fails for various other reasons (these are not important because the construction should *not* be triggered at this point). So in a way the error is expected, and we should probably remove the pr_err for the case where ENOENT is returned for the algorithm that we're currently testing. The solution is two-fold. First when an algorithm undergoes self-testing it should not trigger its construction. Secondly if an instance larval fails to materialise due to it being destroyed by a more optimised algorithm coming along, it should obviously retry the construction. Remove the check in __crypto_alg_lookup that stops a larval from matching new requests based on differences in the mask. It is better to block new requests even if it is wrong and then simply retry the lookup. If this ends up being the wrong larval it will sort iself out during the retry. Reduce the CRYPTO_ALG_TYPE_MASK bits in type during larval creation as otherwise LSKCIPHER algorithms may not match SKCIPHER larvals. Also block the instance creation during self-testing in the function crypto_larval_lookup by checking for CRYPTO_ALG_TESTED in the mask field. Finally change the return value when crypto_alg_lookup fails in crypto_larval_wait to EAGAIN to redo the lookup. Fixes: 37da5d0ffa7b ("crypto: api - Do not wait for tests during registration") Reported-by: Eric Biggers Signed-off-by: Herbert Xu --- crypto/api.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/crypto/api.c b/crypto/api.c index bbe29d438815..bfd177a4313a 100644 --- a/crypto/api.c +++ b/crypto/api.c @@ -70,11 +70,6 @@ static struct crypto_alg *__crypto_alg_lookup(const char *name, u32 type, if ((q->cra_flags ^ type) & mask) continue; - if (crypto_is_larval(q) && - !crypto_is_test_larval((struct crypto_larval *)q) && - ((struct crypto_larval *)q)->mask != mask) - continue; - exact = !strcmp(q->cra_driver_name, name); fuzzy = !strcmp(q->cra_name, name); if (!exact && !(fuzzy && q->cra_priority > best)) @@ -113,6 +108,8 @@ struct crypto_larval *crypto_larval_alloc(const char *name, u32 type, u32 mask) if (!larval) return ERR_PTR(-ENOMEM); + type &= ~CRYPTO_ALG_TYPE_MASK | (mask ?: CRYPTO_ALG_TYPE_MASK); + larval->mask = mask; larval->alg.cra_flags = CRYPTO_ALG_LARVAL | type; larval->alg.cra_priority = -1; @@ -229,7 +226,7 @@ again: type = alg->cra_flags & ~(CRYPTO_ALG_LARVAL | CRYPTO_ALG_DEAD); mask = larval->mask; alg = crypto_alg_lookup(alg->cra_name, type, mask) ?: - ERR_PTR(-ENOENT); + ERR_PTR(-EAGAIN); } else if (IS_ERR(alg)) ; else if (crypto_is_test_larval(larval) && @@ -308,8 +305,12 @@ static struct crypto_alg *crypto_larval_lookup(const char *name, u32 type, if (!IS_ERR_OR_NULL(alg) && crypto_is_larval(alg)) alg = crypto_larval_wait(alg); - else if (!alg) + else if (alg) + ; + else if (!(mask & CRYPTO_ALG_TESTED)) alg = crypto_larval_add(name, type, mask); + else + alg = ERR_PTR(-ENOENT); return alg; }