[PATCH 5/9] crypto, deflate: Implement zbufsize()

[Kees Cook]

This implements the worst-case compression size querying interface for
deflate, based on the logic originally used by pstore.

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 crypto/deflate.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/crypto/deflate.c b/crypto/deflate.c
index 94ec3b36a8e8..2665af8d49b4 100644
--- a/crypto/deflate.c
+++ b/crypto/deflate.c
@@ -277,6 +277,47 @@ static int deflate_sdecompress(struct crypto_scomp *tfm, 
const u8 *src,
        return __deflate_decompress(src, slen, dst, dlen, ctx);
 }
 
+static int __deflate_zbufsize(unsigned int slen, unsigned int *dlen)
+{
+       size_t size = slen;
+       size_t cmpr;
+
+       /* Estimated ranges */
+       switch (size) {
+       case 1000 ... 2000:
+               cmpr = 56;
+               break;
+       case 2001 ... 3000:
+               cmpr = 54;
+               break;
+       case 3001 ... 3999:
+               cmpr = 52;
+               break;
+       case 4000 ... 10000:
+               cmpr = 45;
+               break;
+       default:
+               cmpr = 60;
+               break;
+       }
+
+       *dlen = (size * 100) / cmpr;
+
+       return 0;
+}
+
+static int deflate_zbufsize(struct crypto_tfm *tfm, unsigned int slen,
+                           unsigned int *dlen)
+{
+       return __deflate_zbufsize(slen, dlen);
+}
+
+static int deflate_szbufsize(struct crypto_scomp *tfm, unsigned int slen,
+                            unsigned int *dlen, void *ctx)
+{
+       return __deflate_zbufsize(slen, dlen);
+}
+
 static struct crypto_alg alg = {
        .cra_name               = "deflate",
        .cra_flags              = CRYPTO_ALG_TYPE_COMPRESS,
@@ -285,8 +326,9 @@ static struct crypto_alg alg = {
        .cra_init               = deflate_init,
        .cra_exit               = deflate_exit,
        .cra_u                  = { .compress = {
-       .coa_compress           = deflate_compress,
-       .coa_decompress         = deflate_decompress } }
+       .coa_compress           = deflate_compress,
+       .coa_decompress         = deflate_decompress,
+       .coa_zbufsize           = deflate_zbufsize } }
 };
 
 static struct scomp_alg scomp[] = { {
@@ -294,6 +336,7 @@ static struct scomp_alg scomp[] = { {
        .free_ctx               = deflate_free_ctx,
        .compress               = deflate_scompress,
        .decompress             = deflate_sdecompress,
+       .zbufsize               = deflate_szbufsize,
        .base                   = {
                .cra_name       = "deflate",
                .cra_driver_name = "deflate-scomp",
@@ -304,6 +347,7 @@ static struct scomp_alg scomp[] = { {
        .free_ctx               = deflate_free_ctx,
        .compress               = deflate_scompress,
        .decompress             = deflate_sdecompress,
+       .zbufsize               = deflate_szbufsize,
        .base                   = {
                .cra_name       = "zlib-deflate",
                .cra_driver_name = "zlib-deflate-scomp",
-- 
2.17.1