gzip compressed mbox: Panic: file istream-zlib.c: line 421 (i_stream_zlib_seek): assertion failed: (ret == -1)

[Anton Yuzhaninov]

On 07/05/17 13:25, Aki Tuomi wrote:
>> I use mbox compressed by gzip as read-only folder (using zlib plugin).
>>
>> I have errors in logs:
>> Panic: file istream-zlib.c: line 416 (i_stream_zlib_seek): assertion
>> failed: (ret == -1)
...
>> The bug appeared in 2.2.26 and still can be reproduced (in 2.2.31)
>>
>> Using 'git bisect' was not productive (a lot of build errors), but I've
>> found that reverting this commit:
>> https://github.com/dovecot/core/commit/6a1110d8757bb72fd90f4fe0857fd3aeaf8920ff
>>
>> "fixes" problem for me, so I suppose the bug was introduced in this commit.

> If you only revert the bit here
> 
> 
> -		} while (i_stream_read(&stream->istream) > 0);
> +		} while ((ret = i_stream_read(&stream->istream)) > 0);
> 
> in src/lib-compression/istream-zlib.c
> 
> does it still fix the issue?

With this change applied to fresh origin/master-2.2 I see no error:
--- a/src/lib-compression/istream-zlib.c
+++ b/src/lib-compression/istream-zlib.c
@@ -417,7 +417,7 @@ i_stream_zlib_seek(struct istream_private *stream,
uoff_t v_offset, bool mark)
                        }

                        i_stream_skip(&stream->istream, avail);
-               } while ((ret = i_stream_read(&stream->istream)) > 0);
+               } while (i_stream_read(&stream->istream) > 0);
                i_assert(ret == -1);

                if (stream->istream.v_offset != v_offset) {

But if ret is not assigned, then assert below is useless.

May be better fix will be:
index f7354d83d..06389362a 100644
--- a/src/lib-compression/istream-zlib.c
+++ b/src/lib-compression/istream-zlib.c
@@ -404,7 +404,7 @@ i_stream_zlib_seek(struct istream_private *stream,
uoff_t v_offset, bool mark)
                stream->pos = stream->skip;
        } else {
                /* read and cache forward */
-               ssize_t ret = -1;
+               ssize_t ret;

                do {
                        size_t avail = stream->pos - stream->skip;
@@ -413,6 +413,7 @@ i_stream_zlib_seek(struct istream_private *stream,
uoff_t v_offset, bool mark)
                                i_stream_skip(&stream->istream,
                                              v_offset -
                                              stream->istream.v_offset);
+                               ret = -1;
                                break;
                        }

It also works for me.

Also similar code can be found in files for other compression formats.