Messages in this thread Patch in this message | | | From | Ard Biesheuvel <> | Date | Wed, 30 Jun 2021 11:13:00 +0200 | Subject | Re: [syzbot] BUG: sleeping function called from invalid context in __fdget_pos |
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On Wed, 30 Jun 2021 at 10:10, Herbert Xu <herbert@gondor.apana.org.au> wrote: > > Hi Ard: > > On Wed, Jun 30, 2021 at 09:42:14AM +0200, Ard Biesheuvel wrote: > > > > > There's one suspect-looking site in xts_crypt(): > > > > > > > kernel_fpu_begin(); > > > > > > > > /* calculate first value of T */ > > > > aesni_enc(aes_ctx(ctx->raw_tweak_ctx), walk.iv, walk.iv); > > > > > > > > while (walk.nbytes > 0) { > > > > int nbytes = walk.nbytes; > > > > > > > > ... > > > > > > > > err = skcipher_walk_done(&walk, walk.nbytes - nbytes); > > > > > > > > kernel_fpu_end(); > > > > > > > > if (walk.nbytes > 0) > > > > kernel_fpu_begin(); > > > > } > > > > > > I wonder if a slab allocation failure could leave us with walk.nbytes==0. > > > > The code is actually the other way around: kernel_fpu_end() comes > > before the call to skcipher_walk_done(). > > > > So IIUC, this code forces an allocation failure, and checks whether > > the code deals with this gracefully, right? > > > > The skcipher walk API guarantees that walk.nbytes == 0 if an error is > > returned, so the pairing of FPU begin/end looks correct to me. And > > skcipher_walk_next() should not invoke anything that might sleep from > > this particular context. > > > > Herbert, any ideas? > > xts_crypt looks buggy to me. In particular, if the second > skcipher_walk_virt call (the one in the if clause) fails, then > we will return without calling kernel_fpu_end. > > Another issue, we are not checking for errors on the first > skcipher_walk_virt call, this may cause a double-free with > the subsequent skcipher_walk_abort inside the if clause. > > With skcikpher_walk_virt, you must check for errors explicitly > *unless* you use it in a loop construct which exits on !walk->nbytes. >
So something like this, I suppose?
--- a/arch/x86/crypto/aesni-intel_glue.c +++ b/arch/x86/crypto/aesni-intel_glue.c @@ -849,6 +849,8 @@ return -EINVAL;
err = skcipher_walk_virt(&walk, req, false); + if (err) + return err;
if (unlikely(tail > 0 && walk.nbytes < walk.total)) { int blocks = DIV_ROUND_UP(req->cryptlen, AES_BLOCK_SIZE) - 2; @@ -862,7 +864,10 @@ skcipher_request_set_crypt(&subreq, req->src, req->dst, blocks * AES_BLOCK_SIZE, req->iv); req = &subreq; + err = skcipher_walk_virt(&walk, req, false); + if (err) + return err; } else { tail = 0; }
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