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Message-ID: <20121218224153.GA6143@gmail.com>
Date: Tue, 18 Dec 2012 23:41:53 +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 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);
+ 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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