dovecot - Feb 2017 - Crash while reading compressed mbox: Panic: file istream-zlib.c: line 416 (i_stream_zlib_seek): assertion failed: (ret == -1)

Hello,

I use mbox compressed by gzip as read-only folder (using zlib plugin).

This setup worked for a while, but doesn't work with latest dovecot 
version (2.2.27).

I have error in logs:
Panic: file istream-zlib.c: line 416 (i_stream_zlib_seek): assertion 
failed: (ret == -1)

I can see list of messages in MUA but can't ready body of any message.
I've tried to delete indexes, but it doesn't help.

Backtrace looks like:
(gdb) bt
#0  0x0000000011266a4a in thr_kill () from /lib/libc.so.7
#1  0x0000000011266a1b in raise () from /lib/libc.so.7
#2  0x0000000011266989 in abort () from /lib/libc.so.7
#3  0x0000000010ef3850 in default_fatal_finish (type=LOG_TYPE_PANIC, 
status=0) at failures.c:201
#4  0x0000000010ef5167 in i_internal_fatal_handler (ctx=0x7fffffffe010, 
format=0x1222cf93 "file %s: line %d (%s): assertion failed: (%s)", 
args=0x7fffffffdff0)
     at failures.c:670
#5  0x0000000010ef3e5f in i_panic (format=0x1222cf93 "file %s: line %d 
(%s): assertion failed: (%s)") at failures.c:275
#6  0x0000000012229238 in i_stream_zlib_seek (stream=0x118dd300, 
v_offset=56248, mark=false) at istream-zlib.c:416
#7  0x0000000010f05e48 in i_stream_skip (stream=0x118dd370, count=32489) 
at istream.c:278
#8  0x0000000010f057ba in i_stream_seek (stream=0x118dd370, 
v_offset=56248) at istream.c:300
#9  0x0000000010b17702 in istream_raw_mbox_get_body_size 
(stream=0x118ec870, expected_body_size=36695, 
body_size_r=0x7fffffffe2a0) at istream-raw-mbox.c:612
#10 0x0000000010b2b0aa in mbox_sync_read_next_mail 
(sync_ctx=0x7fffffffe418, mail_ctx=0x7fffffffe270) at mbox-sync.c:162
#11 0x0000000010b2964a in mbox_sync_loop (sync_ctx=0x7fffffffe418, 
mail_ctx=0x7fffffffe270, partial=false) at mbox-sync.c:1057
#12 0x0000000010b290cb in mbox_sync_do (sync_ctx=0x7fffffffe418, 
flags=MBOX_SYNC_UNDIRTY) at mbox-sync.c:1642
#13 0x0000000010b28999 in mbox_sync_int (mbox=0x118ee040, 
flags=MBOX_SYNC_UNDIRTY, lock_id=0x7fffffffe640) at mbox-sync.c:1969
#14 0x0000000010b280ea in mbox_sync (mbox=0x118ee040, 
flags=MBOX_SYNC_UNDIRTY) at mbox-sync.c:2022
#15 0x0000000010b28c9e in mbox_storage_sync_init (box=0x118ee040, 
flags=65) at mbox-sync.c:2071
#16 0x0000000010acc280 in mailbox_sync_init (box=0x118ee040, flags=65) 
at mail-storage.c:1740
#17 0x0000000010acb45d in mailbox_sync (box=0x118ee040, flags=65) at 
mail-storage.c:1788
#18 0x0000000000418cf5 in select_open (ctx=0x1184a1a8, 
mailbox=0x11816f50 "old/Example/INBOX.gz", readonly=false) at 
cmd-select.c:303
#19 0x0000000000418937 in cmd_select_full (cmd=0x1184a040, 
readonly=false) at cmd-select.c:426
#20 0x00000000004190f7 in cmd_select (cmd=0x1184a040) at cmd-select.c:435
#21 0x0000000000423b00 in command_exec (cmd=0x1184a040) at 
imap-commands.c:181
#22 0x00000000004220c0 in client_command_input (cmd=0x1184a040) at 
imap-client.c:986



-- 
Best Regards,
Anton Yuzhaninov