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Date: Fri, 13 May 2016 23:01:09 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: nftw miscalculates FTW.base when pathnames end in /
On Wed, May 04, 2016 at 03:42:19PM +0200, Joakim Sindholt wrote:
> Running the test program from the glibc ftw man page[1]:
>
> +zhasha@...belwind /home/zhasha ; ./6.out test
> d 0 4096 test 0 test
> d 1 4096 test/a 5 a
> f 2 0 test/a/1 7 1
> d 1 4096 test/b 5 b
> f 2 0 test/b/1 7 1
> f 2 0 test/b/2 7 2
> d 1 4096 test/ddd 5 ddd
> f 2 0 test/ddd/5 9 5
> d 1 4096 test/cc 5 cc
> f 2 0 test/cc/3 8 3
> +zhasha@...belwind /home/zhasha ; ./6.out test/
> d 0 4096 test/ 4 /
> d 1 4096 test/a 6
> f 2 0 test/a/1 7 1
> d 1 4096 test/b 6
> f 2 0 test/b/1 7 1
> f 2 0 test/b/2 7 2
> d 1 4096 test/ddd 6 dd
> f 2 0 test/ddd/5 9 5
> d 1 4096 test/cc 6 c
> f 2 0 test/cc/3 8 3
>
> The final 2 columns are the file name length and path + ftw->base
> respectively, which is off by one when the path ends in /. It also
> seems to confuse the initial dir name.
>
> I have attached a fix but I'm not sure it's a particularly good one.
>
> [1] http://linux.die.net/man/3/ftw
> diff --git a/src/misc/nftw.c b/src/misc/nftw.c
> index efb2b89..7c2c0d3 100644
> --- a/src/misc/nftw.c
> +++ b/src/misc/nftw.c
> @@ -108,11 +108,13 @@ int nftw(const char *path, int (*fn)(const char *, const struct stat *, int, str
> if (fd_limit <= 0) return 0;
>
> l = strlen(path);
> + while (l && path[l-1]=='/') --l;
> if (l > PATH_MAX) {
> errno = ENAMETOOLONG;
> return -1;
> }
> - memcpy(pathbuf, path, l+1);
> + memcpy(pathbuf, path, l);
> + pathbuf[l]='\0';
>
> pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
> r = do_nftw(pathbuf, fn, fd_limit, flags, NULL);
Thanks for reminding me to look at this today. I've actually read the
code, and while your patch should avoid the problem, I agree it's
probably not the right fix (interpreting and alterring the part of the
path passed by the application). Instead, I think the error is in the
computations of new.base and lev.base.
new.base should be equal to the offset at which de->d_name is pasted
into the buffer, which is j+1, not l+1; these only differ when path
ends in a slash.
lev.base is computed separately depending on whether or not there's a
previous history; for the no-history case, it should be computed by
skipping all trailing slashes, then backing up until the previous
slash or beginning of string, whichever is hit first. But rather than
special-casing !h in do_nftw, the top-level nftw function should
probably set up a fake "-1 level" history structure to pass in. This
gathers the special top-level logic all in one place.
Can you try these ideas and see if they work for you? If not I'll give
them a try soon, but I've got a few other things I need to do first.
Rich
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