crypto: deflate - fix spurious -ENOSPC

The code in deflate_decompress_one may erroneously return -ENOSPC even if
it didn't run out of output space. The error happens under this
condition:

- Suppose that there are two input pages, the compressed data fits into
  the first page and the zlib checksum is placed in the second page.

- The code iterates over the first page, decompresses the data and fully
  fills the destination buffer, zlib_inflate returns Z_OK becuse zlib
  hasn't seen the checksum yet.

- The outer do-while loop is iterated again, acomp_walk_next_src sets the
  input parameters to the second page containing the checksum.

- We go into the inner do-while loop, execute "dcur =
  acomp_walk_next_dst(&walk);". "dcur" is zero, so we break out of the
  loop and return -ENOSPC, despite the fact that the decompressed data
  fit into the destination buffer.

In order to fix this bug, this commit changes the logic when to report
the -ENOSPC error. We report the error if the destination buffer is empty
*and* if zlib_inflate didn't make any progress consuming the input
buffer. If zlib_inflate consumes the trailing checksum, we see that it
made progress and we will not return -ENOSPC.

Fixes: 08cabc7d3c86 ("crypto: deflate - Convert to acomp")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/deflate.c b/crypto/deflate.c
index 46fc7def8d4cc8eec75d916037bd5625937ea026..710ebba7ce850f8acb28bbcdde821c22eaf8380e 100644 (file)
--- a/crypto/deflate.c
+++ b/crypto/deflate.c
@@ -164,18 +164,21 @@ static int deflate_decompress_one(struct acomp_req *req,
 
                do {
                        unsigned int dcur;
+                       unsigned long avail_in;
 
                        dcur = acomp_walk_next_dst(&walk);
-                       if (!dcur) {
-                               out_of_space = true;
-                               break;
-                       }
 
                        stream->avail_out = dcur;
                        stream->next_out = walk.dst.virt.addr;
+                       avail_in = stream->avail_in;
 
                        ret = zlib_inflate(stream, Z_NO_FLUSH);
 
+                       if (!dcur && avail_in == stream->avail_in) {
+                               out_of_space = true;
+                               break;
+                       }
+
                        dcur -= stream->avail_out;
                        acomp_walk_done_dst(&walk, dcur);
                } while (ret == Z_OK && stream->avail_in);