On 2023/12/27 15:01, Barry Song wrote: > On Wed, Dec 27, 2023 at 7:38 PM Chengming Zhou > <zhouchengming@xxxxxxxxxxxxx> wrote: >> >> 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? >> > > There is no guarrette 2 pages is enough. > > We can invent our own compression algorithm, in our algorithm, we can > add a lot of metadata, for example, longer than 4KB when the source data > is uncompress-able. then dst can be larger than 2 * PAGE_SIZE. but this > is not the case :-) This kind of algorithm may never succeed. > > For those in-tree algorithms, we have a WORST_COMPR_FACTOR. in > ubifs, zram and zswap, we all use "2" as the worst comp factor. Thanks for your explanation! Maybe it's best for us to return to 2 pages if no other people's comments. And this really need more documentation :-) since there is no any comment or check in the acomp compress interface. /* * @src: Source Data * @dst: Destination data * @slen: Size of the input buffer * @dlen: Size of the output buffer and number of bytes produced * @flags: Internal flags * @__ctx: Start of private context data */ struct acomp_req { struct crypto_async_request base; struct scatterlist *src; struct scatterlist *dst; unsigned int slen; unsigned int dlen; u32 flags; void *__ctx[] CRYPTO_MINALIGN_ATTR; }; > > /* > * Some compressors, like LZO, may end up with more data then the input buffer. > * So UBIFS always allocates larger output buffer, to be sure the compressor > * will not corrupt memory in case of worst case compression. > */ > #define WORST_COMPR_FACTOR 2 > > #ifdef CONFIG_FS_ENCRYPTION > #define UBIFS_CIPHER_BLOCK_SIZE FSCRYPT_CONTENTS_ALIGNMENT > #else > #define UBIFS_CIPHER_BLOCK_SIZE 0 > #endif > > /* > * How much memory is needed for a buffer where we compress a data node. > */ > #define COMPRESSED_DATA_NODE_BUF_SZ \ > (UBIFS_DATA_NODE_SZ + UBIFS_BLOCK_SIZE * WORST_COMPR_FACTOR) > > > For years, we have never seen 2 pages that can be a problem. but 1 > page is definitely > not enough, I remember I once saw many cases where accelerators' dmaengine > can write more than 1 page. > >> Thanks. >> >>> >>>> scatterwalk_map_and_copy(scratch->dst, req->dst, 0, req->dlen, >>>> 1); >>> >>> > > Thanks > Barry