On Tue, Nov 28, 2017 at 08:56:59PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> When asked to encrypt or decrypt 0 bytes, both the generic and x86
> implementations of Salsa20 crash in blkcipher_walk_done(), either when
> doing 'kfree(walk->buffer)' or 'free_page((unsigned long)walk->page)',
> because walk->buffer and walk->page have not been initialized.
>
> The bug is that Salsa20 is calling blkcipher_walk_done() even when
> nothing is in 'walk.nbytes'. But blkcipher_walk_done() is only meant to
> be called when a nonzero number of bytes have been provided.
>
> The broken code is part of an optimization that tries to make only one
> call to salsa20_encrypt_bytes() to process inputs that are not evenly
> divisible by 64 bytes. To fix the bug, just remove this "optimization"
> and use the blkcipher_walk API the same way all the other users do.
>
> Reproducer:
>
> #include <linux/if_alg.h>
> #include <sys/socket.h>
> #include <unistd.h>
>
> int main()
> {
> int algfd, reqfd;
> struct sockaddr_alg addr = {
> .salg_type = "skcipher",
> .salg_name = "salsa20",
> };
> char key[16] = { 0 };
>
> algfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
> bind(algfd, (void *)&addr, sizeof(addr));
> reqfd = accept(algfd, 0, 0);
> setsockopt(algfd, SOL_ALG, ALG_SET_KEY, key, sizeof(key));
> read(reqfd, key, sizeof(key));
> }
>
> Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
> Fixes: eb6f13eb9f81 ("[CRYPTO] salsa20_generic: Fix multi-page processing")
> Cc: <stable@xxxxxxxxxxxxxxx> # v2.6.25+
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Patch applied. Thanks.
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
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