On Fri, Dec 29, 2017 at 02:30:19PM -0600, Eric Biggers wrote: > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > 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@xxxxxxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Patch applied. Thanks. -- Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
