Christian Brabandt wrote:
> Hi Dominique!
>
> On Di, 14 Feb 2017, Dominique Pellé wrote:
>
>> Hi
>>
>> afl-fuzz found another command that causes access to
>> invalid memory in Vim-8.0.329. It's not a recent regression
>> since bug is present in at least Vim-7.4.52 that comes
>> with ubuntu-14.04.
>>
>> I have not been able to find a fix yet.
>>
>> Step to reproduce:
>>
>> $ valgrind vim -u NONE -c'norm oxx' -c'norm vapo' -c'q!' 2>vg.log
>>
>> And vg.log contains:
>>
>> ==4259== Memcheck, a memory error detector
>> ==4259== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
>> ==4259== Using Valgrind-3.12.0.SVN and LibVEX; rerun with -h for copyright
>> info
>> ==4259== Command: vim -u NONE -cnorm\ oxx -cnorm\ vapo -cq!
>> ==4259==
>> ==4259== Invalid read of size 1
>> ==4259== at 0x4CF4A0: utf_head_off (mbyte.c:3746)
>> ==4259== by 0x4D094C: mb_adjustpos (mbyte.c:4028)
>> ==4259== by 0x4E11C9: normal_cmd (normal.c:1292)
>> ==4259== by 0x468F25: exec_normal (ex_docmd.c:10418)
>> ==4259== by 0x469076: ex_normal (ex_docmd.c:10310)
>> ==4259== by 0x46B734: do_one_cmd (ex_docmd.c:2981)
>> ==4259== by 0x46B734: do_cmdline (ex_docmd.c:1120)
>> ==4259== by 0x5BFC2B: exe_commands (main.c:2905)
>> ==4259== by 0x5BFC2B: vim_main2 (main.c:781)
>> ==4259== by 0x40C3D3: main (main.c:415)
>> ==4259== Address 0xa95bc50 is 0 bytes after a block of size 4,096 alloc'd
>> ==4259== at 0x4C2ABF5: malloc (vg_replace_malloc.c:299)
>> ==4259== by 0x4C4D0B: lalloc (misc2.c:942)
>> ==4259== by 0x5C0830: mf_alloc_bhdr.isra.3 (memfile.c:907)
>> ==4259== by 0x5C1546: mf_new (memfile.c:381)
>> ==4259== by 0x4AC6FF: ml_new_data (memline.c:3513)
>> ==4259== by 0x4AF0FC: ml_open (memline.c:400)
>> ==4259== by 0x414DD6: open_buffer (buffer.c:163)
>> ==4259== by 0x5BF891: create_windows (main.c:2677)
>> ==4259== by 0x5BF891: vim_main2 (main.c:704)
>> ==4259== by 0x40C3D3: main (main.c:415)
>>
>> Possibly related to this, the following command does not
>> seem to behave correctly, even if it does not trigger invalid
>> memory:
>>
>> $ echo "foo bar" | vim -u NONE -c'norm wvapo' -
>>
>> Then press o multiple times and observe that cursor
>> alternates between the beginning of the visual block
>> and the *middle* of the visual block. I would expect it to
>> alternate between the beginning and the *end* of the
>> visual block.
>
> Interesting. The second issue happens, because current_par does
> internally switch to visual line mode, but does not reset the VIsual
> column correctly. This patch fixes it:
>
> diff --git a/src/search.c b/src/search.c
> index 36410e50f..ffda65837 100644
> --- a/src/search.c
> +++ b/src/search.c
> @@ -4241,6 +4241,7 @@ extend:
> * line, we get stuck there. Trap this here. */
> if (VIsual_mode == 'V' && start_lnum == curwin->w_cursor.lnum)
> goto extend;
> + VIsual.col = 0;
> VIsual.lnum = start_lnum;
> VIsual_mode = 'V';
> redraw_curbuf_later(INVERTED); /* update the inversion */
>
> As a side effect this also disables switching cursor position using 'o'
> which is currently a no-op when only a single line is selected (since it
> effectively switches positions between the start of line and the start
> of line).
>
> Interestingly, I never noticed that this does nothing currently if a
> single visual line is selected.
>
> As it stands, I think this also fixes the invalid read mentioned above.
> I just wanted to take a look at that issue, when I noticed that this
> patch does not exhibit this behaviour, so I didn't check very closely
> why it works.
>
> I tried to add a test, to verify that this is fixed, but whatever I do,
> I always get back col 0 for the visual mode. I think this is because in
> getmark_buf_fnum() (mark.c:417) the column is explicitly set to zero for
> visual line mode and also using getpos('v') does not work, since by the
> time I run it, Visual mode is no longer active, so I cannot verify that
> this works in vimscript.
Hi Christian
Your patch appears to fix the valgrind error.
However, it's not correct. If I do...
$ echo "foo bar" | vim -u NONE -c'norm wvapo' -
... then pressing o multiple times, the cursor remains
at the beginning of the visual selection, instead of
alternating at the beginning and at the end of the
visual selection.
Regards
Dominique
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