On 2023/12/27 14:25, Barry Song wrote: > On Wed, Dec 27, 2023 at 4:51 PM Chengming Zhou > <zhouchengming@xxxxxxxxxxxxx> wrote: >> >> On 2023/12/27 08:23, Nhat Pham wrote: >>> On Tue, Dec 26, 2023 at 3:30 PM Chris Li <chrisl@xxxxxxxxxx> wrote: >>>> >>>> Again, sorry I was looking at the decompression side rather than the >>>> compression side. The compression side does not even offer a safe >>>> version of the compression function. >>>> That seems to be dangerous. It seems for now we should make the zswap >>>> roll back to 2 page buffer until we have a safe way to do compression >>>> without overwriting the output buffers. >>> >>> Unfortunately, I think this is the way - at least until we rework the >>> crypto/compression API (if that's even possible?). >>> I still think the 2 page buffer is dumb, but it is what it is :( >> >> Hi, >> >> I think it's a bug in `scomp_acomp_comp_decomp()`, which doesn't use >> the caller passed "src" and "dst" scatterlist. Instead, it uses its own >> per-cpu "scomp_scratch", which have 128KB src and dst. >> >> When compression done, it uses the output req->dlen to copy scomp_scratch->dst >> to our dstmem, which has only one page now, so this problem happened. >> >> I still don't know why the alg->compress(src, slen, dst, &dlen) doesn't >> check the dlen? It seems an obvious bug, right? >> >> As for this problem in `scomp_acomp_comp_decomp()`, this patch below >> should fix it. I will set up a few tests to check later. >> >> Thanks! >> >> diff --git a/crypto/scompress.c b/crypto/scompress.c >> index 442a82c9de7d..e654a120ae5a 100644 >> --- a/crypto/scompress.c >> +++ b/crypto/scompress.c >> @@ -117,6 +117,7 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir) >> struct crypto_scomp *scomp = *tfm_ctx; >> void **ctx = acomp_request_ctx(req); >> struct scomp_scratch *scratch; >> + unsigned int dlen; >> int ret; >> >> if (!req->src || !req->slen || req->slen > SCOMP_SCRATCH_SIZE) >> @@ -128,6 +129,8 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir) >> if (!req->dlen || req->dlen > SCOMP_SCRATCH_SIZE) >> req->dlen = SCOMP_SCRATCH_SIZE; >> >> + dlen = req->dlen; >> + >> scratch = raw_cpu_ptr(&scomp_scratch); >> spin_lock(&scratch->lock); >> >> @@ -145,6 +148,9 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir) >> ret = -ENOMEM; >> goto out; >> } >> + } else if (req->dlen > dlen) { >> + ret = -ENOMEM; >> + goto out; >> } > > This can't fix the problem as crypto_scomp_compress() has written overflow data. No, crypto_scomp_compress() writes to its own scomp_scratch->dst memory, then copy to our dstmem. > > BTW, in many cases, hardware-accelerators drivers/crypto can do compression and > decompression by off-loading CPU; > we won't have a chance to let hardware check the dst buffer size. so > giving the dst buffer > with enough length to the hardware's dma engine is the right way. I > mean, we shouldn't > change dst from 2pages to 1page. But how do we know 2 pages is enough for any compression algorithm? Thanks. > >> scatterwalk_map_and_copy(scratch->dst, req->dst, 0, req->dlen, >> 1); > > > Thanks > Barry