Quick and dirty malloc() support for realpath.

[Mike Frysinger]

On Tuesday 27 October 2009 15:44:42 Rob Landley wrote:
> On Tuesday 27 October 2009 05:51:05 Bernhard Reutner-Fischer wrote:
> > On Tue, Oct 27, 2009 at 08:54:50AM +0100, Ricard Wanderlof wrote:
> > >On Mon, 26 Oct 2009, Rob Landley wrote:
> > >>... Also, in my experience _Bool is about as real-world useful as
> > >>the bit field notation with the colons, and is really there to keep
> > >>the language pedants and the c++ guys happy without actually
> > >>accomplishing much.  I've never seen it actually produce better
> > >>code.
> > >
> > >It can produce more readable, less error-prone C code though. We use
> >
> > $ size libc/stdlib/realpath.o*
> >    text	   data	    bss	    dec	    hex	filename
> >     555	      0	      0	    555	    22b	libc/stdlib/realpath.os.oorig
> >     735	      0	      0	    735	    2df	libc/stdlib/realpath.os.rob
> >     586	      0	      0	    586	    24a	libc/stdlib/realpath.os
> >
> > perhaps that would do as well and doesn't cost 180b (!) but about 31b..
> 
> The problem is that leaks memory if realpath ever returns failure, such as
>  the lines right after that patch:

our friend goto solves the leak.  stick it in the middle of the file to 
maximize short forward/backward jumps and we only get a small increase:

    578       0       0     578     242 libc/stdlib/realpath.os.orig
    609       0       0     609     261 libc/stdlib/realpath.os

diff --git a/libc/stdlib/realpath.c b/libc/stdlib/realpath.c
index 1a00c31..146d1d8 100644
--- a/libc/stdlib/realpath.c
+++ b/libc/stdlib/realpath.c
@@ -47,8 +47,7 @@ char got_path[];
 	char copy_path[PATH_MAX];
 	/* use user supplied buffer directly - reduces stack usage */
 	/* char got_path[PATH_MAX]; */
-	char *max_path;
-	char *new_path;
+	char *max_path, *new_path, *allocated_path;
 	size_t path_len;
 	int readlinks = 0;
 #ifdef S_IFLNK
@@ -72,12 +71,13 @@ char got_path[];
 	/* Copy so that path is at the end of copy_path[] */
 	strcpy(copy_path + (PATH_MAX-1) - path_len, path);
 	path = copy_path + (PATH_MAX-1) - path_len;
+	allocated_path = got_path ? NULL : malloc(PATH_MAX);
 	max_path = got_path + PATH_MAX - 2; /* points to last non-NUL char */
 	new_path = got_path;
 	if (*path != '/') {
 		/* If it's a relative pathname use getcwd for starters. */
 		if (!getcwd(new_path, PATH_MAX - 1))
-			return NULL;
+			goto err;
 		new_path += strlen(new_path);
 		if (new_path[-1] != '/')
 			*new_path++ = '/';
@@ -114,6 +114,8 @@ char got_path[];
 		while (*path != '\0' && *path != '/') {
 			if (new_path > max_path) {
 				__set_errno(ENAMETOOLONG);
+ err:
+				free(allocated_path);
 				return NULL;
 			}
 			*new_path++ = *path++;
@@ -122,7 +124,7 @@ char got_path[];
 		/* Protect against infinite loops. */
 		if (readlinks++ > MAX_READLINKS) {
 			__set_errno(ELOOP);
-			return NULL;
+			goto err;
 		}
 		path_len = strlen(path);
 		/* See if last (so far) pathname component is a symlink. */
@@ -133,13 +135,13 @@ char got_path[];
 			if (link_len < 0) {
 				/* EINVAL means the file exists but isn't a symlink. */
 				if (errno != EINVAL) {
-					return NULL;
+					goto err;
 				}
 			} else {
 				/* Safe sex check. */
 				if (path_len + link_len >= PATH_MAX - 2) {
 					__set_errno(ENAMETOOLONG);
-					return NULL;
+					goto err;
 				}
 				/* Note: readlink doesn't add the null byte. */
 				/* copy_path[link_len] = '\0'; - we don't need it too */
-mike
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