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Date: Tue, 18 Dec 2012 23:50:11 +0100
From: Cong Ding <dinggnu@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Jiri Kosina <jkosina@...e.cz>, Jesper Juhl <jj@...esealer.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usr/gen_init_cpio.c: remove unnecessary "if"
On Tue, Dec 18, 2012 at 11:41:53PM +0100, Cong Ding wrote:
> On Tue, Dec 18, 2012 at 02:03:08PM -0800, Kees Cook wrote:
> > [resend, busted mailer]
> >
> > On Tue, Dec 18, 2012 at 1:26 PM, Cong Ding <dinggnu@...il.com> wrote:
> > >
> > > usr/gen_init_cpio.c: remove unnecessary "if"
> > >
> > > if it goes to fail, dname isn't allocated; otherwise, it is allocated
> > > successfully. so we just free memory when it doesn't fail.
> > >
> > > this patch also fix a trival trailing space warning by checkpatch
> > >
> > > Signed-off-by: Cong Ding <dinggnu@...il.com>
> > > ---
> > > usr/gen_init_cpio.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> > > index af8c925..afebe09 100644
> > > --- a/usr/gen_init_cpio.c
> > > +++ b/usr/gen_init_cpio.c
> > > @@ -372,7 +372,7 @@ static int cpio_mkfile(const char *name, const char
> > > *location,
> > > }
> > > ino++;
> > > rc = 0;
> > > -
> > > +
> > > error:
> > > if (filebuf) free(filebuf);
> > > if (file >= 0) close(file);
> >
> >
> > This chunk is fine.
> >
> > > @@ -452,8 +452,8 @@ static int cpio_mkfile_line(const char *line)
> > > }
> > > rc = cpio_mkfile(dname, cpio_replace_env(location),
> > > mode, uid, gid, nlinks);
> > > + free(dname);
> > > fail:
> > > - if (dname_len) free(dname);
> > > return rc;
> > > }
> >
> > While technically correct, the dname_len check is there to avoid the case of
> > trying to free "name" if a "goto fail" is ever added to the code. So, it's
> > defensive given the mixing of dname being either allocated or static. I
> > think it might be cleaner to use a new char * (maybe "name_arg", instead of
> > re-using dname), and then dname can always be freed before the function
> > returns:
> >
> > char * name_arg;
> > ...
> > if (end && ...) {
> > ...
> > name_arg = dname;
> > } else {
> > name_arg = name;
> > }
> > rc = cpio_mkfile(name_arg, ...);
> > fail:
> > free(dname);
> > return rc;
> sorry my patch is wrong (I missed the "else" branch). but I don't think it is
> necessary to use another variable name_arg. so I think the correct version
> would be as following. if you think it is necessary and agree the change, I
> will send a version 2.
>
> @@ -452,8 +452,8 @@ static int cpio_mkfile_line(const char *line)
> }
> rc = cpio_mkfile(dname, cpio_replace_env(location),
> mode, uid, gid, nlinks);
> + if (dname_len) free(dname);
> - fail:
> + out:
> - if (dname_len) free(dname);
> return rc;
> }
>
> or you want something like this? I have added variable name_arg, changed the
> dname_len to name_len, changed fail to out, moved free(dname) before "out".
> (btw, if we do like this, what do you suggest to use in the commit message?)
>
> usr/gen_init_cpio.c | 26 ++++++++++++++------------
> 1 file changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> index af8c925..dff6a1e 100644
> --- a/usr/gen_init_cpio.c
> +++ b/usr/gen_init_cpio.c
> @@ -409,19 +409,20 @@ static int cpio_mkfile_line(const char *line)
> {
> char name[PATH_MAX + 1];
> char *dname = NULL; /* malloc'ed buffer for hard links */
> + char *name_arg;
> char location[PATH_MAX + 1];
> unsigned int mode;
> int uid;
> int gid;
> int nlinks = 1;
> - int end = 0, dname_len = 0;
> + int end = 0, name_len = 0;
> int rc = -1;
>
> if (5 > sscanf(line, "%" str(PATH_MAX) "s %" str(PATH_MAX)
> "s %o %d %d %n",
> name, location, &mode, &uid, &gid, &end)) {
> fprintf(stderr, "Unrecognized file format '%s'", line);
> - goto fail;
> + goto out;
> }
> if (end && isgraph(line[end])) {
> int len;
> @@ -429,12 +430,13 @@ static int cpio_mkfile_line(const char *line)
>
> dname = malloc(strlen(line));
> if (!dname) {
> - fprintf (stderr, "out of memory (%d)\n", dname_len);
> - goto fail;
> + fprintf (stderr, "out of memory (%d)\n", name_len);
another thing I forgot to mention is that this the value of name_len in
fprintf is always 0. So can I assume here is something wrong? maybe we should
use this?
fprintf (stderr, "out of memory (%d)\n", strlen(line));
> + goto out;
> }
>
> - dname_len = strlen(name) + 1;
> - memcpy(dname, name, dname_len);
> + name_arg = dname;
> + name_len = strlen(name) + 1;
> + memcpy(name_arg, name, name_len);
>
> do {
> nend = 0;
> @@ -442,18 +444,18 @@ static int cpio_mkfile_line(const char *line)
> name, &nend) < 1)
> break;
> len = strlen(name) + 1;
> - memcpy(dname + dname_len, name, len);
> - dname_len += len;
> + memcpy(name_arg + name_len, name, len);
> + name_len += len;
> nlinks++;
> end += nend;
> } while (isgraph(line[end]));
> } else {
> - dname = name;
> + name_arg = name;
> }
> - rc = cpio_mkfile(dname, cpio_replace_env(location),
> + rc = cpio_mkfile(name_arg, cpio_replace_env(location),
> mode, uid, gid, nlinks);
> - fail:
> - if (dname_len) free(dname);
> + if (!dname) free(dname);
> + out:
> return rc;
> }
>
> --
> 1.7.10.4
>
>
>
>
>
> --
> 1.7.10.4
>
> >
> > And I'd probably rename "fail" to "out".
> >
> > -Kees
> >
> > --
> > Kees Cook
> > Chrome OS Security
--
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