Messages in this thread | | | Date | Wed, 30 Jun 2021 16:09:34 +0800 | From | Herbert Xu <> | Subject | Re: [syzbot] BUG: sleeping function called from invalid context in __fdget_pos |
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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.
Thanks, -- Email: Herbert Xu <herbert@gondor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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