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Message-ID: <20220512130008.GI7074@brightrain.aerifal.cx>
Date: Thu, 12 May 2022 09:00:08 -0400
From: Rich Felker <dalias@...c.org>
To: Ismael Luceno <ismael@...ev.co.uk>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH v3 1/2] nftw: implement FTW_CHDIR
On Sun, Jan 23, 2022 at 04:59:54PM +0100, Ismael Luceno wrote:
> Signed-off-by: Ismael Luceno <ismael@...ev.co.uk>
> ---
> src/misc/nftw.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/src/misc/nftw.c b/src/misc/nftw.c
> index 5b233b2b8e77..7569a657e54e 100644
> --- a/src/misc/nftw.c
> +++ b/src/misc/nftw.c
> @@ -87,6 +87,14 @@ static int do_nftw(char *path, int (*fn)(const char *, const struct stat *, int,
> DIR *d = fdopendir(dfd);
> if (d) {
> struct dirent *de;
> + if (flags & FTW_CHDIR) {
> + if (!fchdir(dfd)) {
> + err = errno;
> + closedir(d);
> + errno = err;
> + return -1;
> + }
> + }
> while ((de = readdir(d))) {
> if (de->d_name[0] == '.'
> && (!de->d_name[1]
I'm not sure how this works -- after the fchdir, subsequent open at
line 69 will fail because the pathname is no longer valid relative to
the new working directory. I think different logic is needed at that
point too in order to adjust the argument to open depending on
FTW_CHDIR (or the whole thing could be converted to using at
functions, but that's a much bigger change I'd really only want to do
in a full overhaul of this function). I'm guessing you only tested
with absolute pathnames.
> @@ -123,6 +131,7 @@ int nftw(const char *path, int (*fn)(const char *, const struct stat *, int, str
> int r, cs;
> size_t l;
> char pathbuf[PATH_MAX+1];
> + int orig_dfd;
>
> if (fd_limit <= 0) return 0;
>
> @@ -133,9 +142,22 @@ int nftw(const char *path, int (*fn)(const char *, const struct stat *, int, str
> }
> memcpy(pathbuf, path, l+1);
>
> + if (flags & FTW_CHDIR) {
> + orig_dfd = open(".", O_CLOEXEC | O_PATH);
> + if (orig_dfd < 0)
> + return -1;
> + }
> +
> pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
> r = do_nftw(pathbuf, fn, fd_limit, flags, NULL);
> pthread_setcancelstate(cs, 0);
> + if (flags & FTW_CHDIR) {
> + if (!fchdir(orig_dfd))
> + r = -1;
> + int err = errno;
> + close(orig_dfd);
> + errno = err;
> + }
> return r;
> }
>
> --
> 2.33.0
The added open and close calls need to be inside the range where
cancellation is blocked. Otherwise they will cause nftw to act on
cancellation.
Rich
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