On 20.10.13 08:05, Ondřej Bílka wrote:
> On Sun, Oct 20, 2013 at 07:47:06AM +0200, Torsten Bögershausen wrote:
>> (may be s/path is too big/path is too long/ ?)
>>
>> On 19.10.13 12:52, Antoine Pelisse wrote:
>>> Currently, most buffers created with PATH_MAX length, are not checked
>>> when being written, and can overflow if PATH_MAX is not big enough to
>>> hold the path.
>>>
>>> Fix that by using strlcpy() where strcpy() was used, and also run some
>>> extra checks when copy is done with memcpy().
>>>
>>> Reported-by: Wataru Noguchi <wnoguchi.0...@gmail.com>
>>> Signed-off-by: Antoine Pelisse <apeli...@gmail.com>
>>> ---
>>> diff --git a/abspath.c b/abspath.c
>>> index 64adbe2..0e60ba4 100644
>>> --- a/abspath.c
>>> +++ b/abspath.c
>>> @@ -216,11 +216,15 @@ const char *absolute_path(const char *path)
>>> const char *prefix_filename(const char *pfx, int pfx_len, const char *arg)
>>> {
>>> static char path[PATH_MAX];
>
> Why do you need static there?
Good point.
get_pathname() from path.c may be better.
>>> +
>>> + if (pfx_len > PATH_MAX)
>> I think this should be
>> if (pfx_len > PATH_MAX-1) /* Keep 1 char for '\0'
>>> + die("Too long prefix path: %s", pfx);
>>> +
>>> #ifndef GIT_WINDOWS_NATIVE
>>> if (!pfx_len || is_absolute_path(arg))
>>> return arg;
>>> memcpy(path, pfx, pfx_len);
>>> - strcpy(path + pfx_len, arg);
>>> + strlcpy(path + pfx_len, arg, PATH_MAX - pfx_len);
>>
>> I'm not sure how to handle overlong path in general, there are several ways:
>> a) Silently overwrite memory (with help of memcpy() and/or strcpy()
>> b) Silently shorten the path using strlcpy() instead of strcpy()
>> c) Avoid the overwriting and call die().
>> d) Prepare a longer buffer using xmalloc()
>>
> There is also
> e) modify allocation to place write protected page after buffer end.
Yes, I think this is what electric fence, DUMA or valgrind do:
http://sourceforge.jp/projects/freshmeat_efence/
http://duma.sourceforge.net/
http://valgrind.sourceforge.net/
Theses are very good tools for developers, finding memory corruption
(or other bugs like using uninitialized memory).
One of the motivation I asked for test cases is that a git developer can
run these test cases under valgrind and can verify that we are never out of
range.
For an end user a git "crash" caused by trying to write to a write protected
page
is better than silently corrupting memory.
And a range check, followed by die(), is even easier to debug.
For an end user.
/Torsten
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