Bug#850058: libass5: mpv often segfaults when displaying status info

[Frédéric Brière]

Package: libass5
Version: 0.13.5-1
Severity: important

After upgrading libass5 to 0.13.5-1, mpv routinely segfaults when
issueing commands that display some status information.  For example, it
always segfaults immediately on P (display progress bar) or PgUp/Down
(next/previous chapter), and is more-or-less likely to crash on other
commands as well.

I also get a slew of those messages whenever the bottom status/progress
bar is displayed:

  [osd/libass] [0x7f54500714d0]: Warning: no style named 'Default' found

Downgrading to 0.13.4-1 fixes both issues.


Here's the relevant backtrace; let me know if there's anything else that
could be helpful.

#0  0x00007f292e24b496 in strlen () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007f292e24b1ce in strdup () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x00007f29308df40b in reset_render_context (
    render_priv=render_priv at entry=0x7f2900af2eb0, style=<optimized out>, 
    style at entry=0x0) at ass_render.c:853
#3  0x00007f29308dfb7a in init_render_context (event=0x7f2900def260, 
    render_priv=0x7f2900af2eb0) at ass_render.c:888
#4  ass_render_event (event_images=0x7f2900df1ed8, event=0x7f2900def260, 
    render_priv=0x7f2900af2eb0) at ass_render.c:2459
#5  ass_render_frame (priv=0x7f2900af2eb0, track=<optimized out>, 
    now=now at entry=0, detect_change=detect_change at entry=0x7f2909a8f624)
    at ass_render.c:3015
#6  0x00005611023cb7bd in append_ass (res=res at entry=0x5611041d09e0, 
    img_list=0x7f2900aea0d0, changed=changed at entry=0x5611041d0a00, 
    ass=<optimized out>, ass=<optimized out>) at ../sub/osd_libass.c:526
#7  0x00005611023cbda2 in osd_object_get_bitmaps (
    osd=osd at entry=0x5611041c5d50, obj=obj at entry=0x5611041d0990, 
    format=format at entry=1, out_imgs=out_imgs at entry=0x7f2909a8f7a0)
    at ../sub/osd_libass.c:541
#8  0x00005611023cae63 in render_object (out_imgs=0x7f2909a8f7a0, 
    sub_formats=0x7f290035fd20, video_pts=0.40040000000000003, res=..., 
    obj=0x5611041d0990, osd=0x5611041c5d50) at ../sub/osd.c:287
#9  osd_draw (osd=0x5611041c5d50, res=..., video_pts=0.40040000000000003, 
    draw_flags=<optimized out>, formats=formats at entry=0x7f290035fd20, 
    cb=cb at entry=0x5611023ecb80 <gen_osd_cb>, 
    cb_ctx=cb_ctx at entry=0x7f290035fcc0) at ../sub/osd.c:329
#10 0x00005611023ed7f1 in mpgl_osd_generate (ctx=0x7f290035fcc0, res=..., 
    pts=<optimized out>, stereo_mode=0, draw_flags=<optimized out>)
    at ../video/out/opengl/osd.c:337
#11 0x00005611023f50f8 in pass_draw_osd (p=p at entry=0x7f2900339ca0, 
    draw_flags=<optimized out>, pts=<optimized out>, rect=..., vp_w=624, 
    vp_h=-362, fbo=fbo at entry=0, cms=cms at entry=true)
    at ../video/out/opengl/video.c:2265
#12 0x00005611023fb37f in gl_video_render_frame (p=0x7f2900339ca0, 
    frame=frame at entry=0x7f2900aefc60, fbo=0)
    at ../video/out/opengl/video.c:2774
#13 0x0000561102402f15 in draw_frame (vo=<optimized out>, frame=0x7f2900aefc60)
    at ../video/out/vo_opengl.c:133
#14 0x000056110240051f in render_frame (vo=0x5611041f47e0)
    at ../video/out/vo.c:814
#15 vo_thread (ptr=0x5611041f47e0) at ../video/out/vo.c:914
#16 0x00007f2933178464 in start_thread ()
   from /lib/x86_64-linux-gnu/libpthread.so.0
#17 0x00007f292e2b39df in clone () from /lib/x86_64-linux-gnu/libc.so.6


-- System Information:
Debian Release: stretch/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.8.0-2-amd64 (SMP w/3 CPU cores)
Locale: LANG=en_CA.UTF-8, LC_CTYPE=en_CA.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)

Versions of packages libass5 depends on:
ii  libc6           2.24-8
ii  libfontconfig1  2.11.0-6.7
ii  libfreetype6    2.6.3-3+b1
ii  libfribidi0     0.19.7-1
ii  libharfbuzz0b   1.2.7-1+b1

libass5 recommends no packages.

libass5 suggests no packages.

-- no debconf information