Re: [PATCH] usr/gen_init_cpio.c: remove unnecessary "if"

[Cong Ding <dinggnu@gmail.com>]

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@gmail.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@gmail.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