Subject: Re: [PATCH] mingw-multibyte: fix memory acces violation and path length limits.

From: Wataru Noguchi <[email-masked]>
Date: Sun, 29 Sep 2013 11:56:28 +0900

Hi,

Thanks for comments.

My currently working repository is

https://github.com/wnoguchi/git/tree/hotfix/mingw-multibyte-path-checkout-failure

I have revert commits to 1f10da3.
I'll try failure step.

- gcc optimization level is O2.(fail)
- gcc O0, O1 works fine.

$ gdb git-clone
GNU gdb 6.8
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-pc-mingw32"...
(gdb) r https://github.com/wnoguchi/mingw-checkout-crash.git
Starting program: C:\msysgit\git/git-clone.exe https://github.com/wnoguchi/mingw
-checkout-crash.git
[New thread 800.0xa10]
Error: dll starting at 0x779f0000 not found.
Error: dll starting at 0x75900000 not found.
Error: dll starting at 0x779f0000 not found.
Error: dll starting at 0x778f0000 not found.
[New thread 800.0x92c]
Cloning into 'mingw-checkout-crash'...
Error: dll starting at 0x29f0000 not found.
remote: Counting objects: 8, done.
remote: Compressing objects: 100% (7/7), done.
remote: Total 8 (delta 0), reused 8 (delta 0)
Unpacking objects: 100% (8/8), done.
Checking connectivity... done
[New thread 800.0xea0]

Program received signal SIGSEGV, Segmentation fault.
0x004d5200 in git_check_attr (
     path=0xacc6a0 ""..., num=5, check=0x572440) at attr.c:754
754                     const char *value = check_all_attr[check[i].attr->attr_n
r].value;
(gdb) list
749             int i;
750
751             collect_all_attrs(path);
752
753             for (i = 0; i < num; i++) {
754                     const char *value = check_all_attr[check[i].attr->attr_n
r].value;
755                     if (value == ATTR__UNKNOWN)
756                             value = ATTR__UNSET;
757                     check[i].value = value;
758             }
(gdb) up
#1  0x004a796b in convert_attrs (ca=0x28f950,
     path=0xacc6a0 ""...) at convert.c:740
740             if (!git_check_attr(path, NUM_CONV_ATTRS, ccheck)) {
(gdb) list
735                             ccheck[i].attr = git_attr(conv_attr_name[i]);
736                     user_convert_tail = &user_convert;
737                     git_config(read_convert_config, NULL);
738             }
739
740             if (!git_check_attr(path, NUM_CONV_ATTRS, ccheck)) {
741                     ca->crlf_action = git_path_check_crlf(path, ccheck + 4);

742                     if (ca->crlf_action == CRLF_GUESS)
743                             ca->crlf_action = git_path_check_crlf(path, cche
ck + 0);
744                     ca->ident = git_path_check_ident(path, ccheck + 1);
(gdb) list -
725             int i;
726             static struct git_attr_check ccheck[NUM_CONV_ATTRS];
727
728     //      if (NUM_CONV_ATTRS != 0) {
729     //              ccheck[0].attr = NULL;
730     //              ccheck[0].value = NULL;
731     //      }
732
733             if (!ccheck[0].attr) {
734                     for (i = 0; i < NUM_CONV_ATTRS; i++)
(gdb) p ccheck[0].attr
$1 = (struct git_attr *) 0xa081e38f

Next, change PATH_MAX value to 4096 if MinGW environment.(6cae216)
Works fine.
Is this failure caused by PATH_MAX length too short? or my repository directory depth too deep?
But when optimization disabled(O0) in Makefile , works fine...(bf0acff)
Do you know what's happen?

Thanks.

(2013/09/29 8:18), Johannes Schindelin wrote:
> Hi,
>
> On Sun, 29 Sep 2013, Wataru Noguchi wrote:
>
>> --- a/convert.c
>> +++ b/convert.c
>> @@ -724,6 +724,11 @@ static void convert_attrs(struct conv_attrs *ca, const char *path)
>>   {
>>   	int i;
>>   	static struct git_attr_check ccheck[NUM_CONV_ATTRS];
>> +	
>> +	if (NUM_CONV_ATTRS != 0) {
>> +		ccheck[0].attr = NULL;
>> +		ccheck[0].value = NULL;
>> +	}
>
> I wonder whether it would make more sense to use
>
> 	memset(ccheck, 0, sizeof(ccheck))
>
> ? But then, ccheck is static and *should* be initialized to all 0
> according to the C standard. And re-initializing it to NULL would
> invalidate the values that were set earlier.
>
> Also, if NUM_CONV_ATTRS == 0, I would expect
>
>>   	if (!ccheck[0].attr) {
>
> to access an invalid location...
>
>> diff --git a/git-compat-util.h b/git-compat-util.h
>> index a31127f..ba02c69 100644
>> --- a/git-compat-util.h
>> +++ b/git-compat-util.h
>> @@ -237,6 +237,16 @@ extern char *gitbasename(char *);
>>   #ifndef PATH_MAX
>>   #define PATH_MAX 4096
>>   #endif
>> +#ifdef GIT_WINDOWS_NATIVE
>> +/* Git for Windows checkout PATH_MAX is reduce to 260.
>> + * but if checkout relative long path name, its length too short.
>> + * thus, expand length.
>> + */
>> +#ifdef PATH_MAX
>> +#undef PATH_MAX
>> +#endif
>> +#define PATH_MAX 4096
>> +#endif
>
> This looks fine, but I am wary... did you not say that a crash was caused
> by this? In that case, we would have a user that accesses the respective
> buffer without checking the size and we would still have to fix that bug..
>
> Ciao,
> Dscho
>

-- 
=========================================
   Wataru Noguchi
   [email-masked]
   http://wnoguchi.github.io/
=========================================

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