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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> Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.