dovecot - Jul 2017 - gzip compressed mbox: Panic: file istream-zlib.c: line 421 (i_stream_zlib_seek): assertion failed: (ret == -1)

Hello,

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)
and can't read messages in MUA.

IMAP commands to reproduce a bug:

1 SELECT "compressed.gz"
2 UID fetch 2 BODY.PEEK[]
# sleep 5
3 UID fetch 2 BODY.PEEK[]
# repeat sleep/fetch until assert (a few fetches need to trigger bug,
probably because of caching)

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.

-- 
Best Regards,
Anton Yuzhaninov

> On July 5, 2017 at 6:38 PM Anton Yuzhaninov <citrin at citrin.ru>
wrote:
> 
> 
> Hello,
> 
> 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)
> and can't read messages in MUA.
> 
> IMAP commands to reproduce a bug:
> 
> 1 SELECT "compressed.gz"
> 2 UID fetch 2 BODY.PEEK[]
> # sleep 5
> 3 UID fetch 2 BODY.PEEK[]
> # repeat sleep/fetch until assert (a few fetches need to trigger bug,
> probably because of caching)
> 
> 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.
> 
> -- 
> Best Regards,
> Anton Yuzhaninov
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?

Aki

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.