Re: [msysGit] [PATCH] Prevent buffer overflows when path is too big
- From
Ondřej Bílka <neleai@seznam.cz>
- Date
- Oct 20, 2013, 07:39 UTC
- Message-ID
- <20131020073905.GA10718@domone.podge>
- In-Reply-To
- <526377C1.8020907@web.de>
On Sun, Oct 20, 2013 at 08:27:13AM +0200, Torsten Bögershausen wrote:
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> 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.0727@gmail.com>
> >>> Signed-off-by: Antoine Pelisse <apelisse@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:
> You need to be selective which buffers are important.
> http://sourceforge.jp/projects/freshmeat_efence/ > http://duma.sourceforge.net/
These are toys, this comes with fact that they need a 8kb of space for each 8byte malloc. Just run a git diff and differences are huge.
$ /usr/bin/time git diff HEAD^ > x 0.06user 0.01system 0:00.07elapsed 97%CPU (0avgtext+0avgdata 19172maxresident)k 0inputs+8outputs (0major+5591minor)pagefaults 0swaps $ LD_PRELOAD=libefence.so /usr/bin/time git diff HEAD^ > x
Electric Fence 2.2 Copyright (C) 1987-1999 Bruce Perens <bruce@perens.com> 3.49user 0.94system 0:04.45elapsed 99%CPU (0avgtext+0avgdata 91920maxresident)k 0inputs+8outputs (0major+118069minor)pagefaults 0swaps
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> 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 >