Merge branch 'strscpy' of git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile

Pull strscpy string copy function implementation from Chris Metcalf.

Chris sent this during the merge window, but I waffled back and forth on
the pull request, which is why it's going in only now.

The new "strscpy()" function is definitely easier to use and more secure
than either strncpy() or strlcpy(), both of which are horrible nasty
interfaces that have serious and irredeemable problems.

strncpy() has a useless return value, and doesn't NUL-terminate an
overlong result.  To make matters worse, it pads a short result with
zeroes, which is a performance disaster if you have big buffers.

strlcpy(), by contrast, is a mis-designed "fix" for strlcpy(), lacking
the insane NUL padding, but having a differently broken return value
which returns the original length of the source string.  Which means
that it will read characters past the count from the source buffer, and
you have to trust the source to be properly terminated.  It also makes
error handling fragile, since the test for overflow is unnecessarily
subtle.

strscpy() avoids both these problems, guaranteeing the NUL termination
(but not excessive padding) if the destination size wasn't zero, and
making the overflow condition very obvious by returning -E2BIG.  It also
doesn't read past the size of the source, and can thus be used for
untrusted source data too.

So why did I waffle about this for so long?

Every time we introduce a new-and-improved interface, people start doing
these interminable series of trivial conversion patches.

And every time that happens, somebody does some silly mistake, and the
conversion patch to the improved interface actually makes things worse.
Because the patch is mindnumbing and trivial, nobody has the attention
span to look at it carefully, and it's usually done over large swatches
of source code which means that not every conversion gets tested.

So I'm pulling the strscpy() support because it *is* a better interface.
But I will refuse to pull mindless conversion patches.  Use this in
places where it makes sense, but don't do trivial patches to fix things
that aren't actually known to be broken.

* 'strscpy' of git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile:
  tile: use global strscpy() rather than private copy
  string: provide strscpy()
  Make asm/word-at-a-time.h available on all architectures

1 files changed, 4 insertions, 29 deletions

diff --git a/arch/tile/gxio/mpipe.c b/arch/tile/gxio/mpipe.c
index ee186e13dfe6..f102048d9c0e 100644
--- a/arch/tile/gxio/mpipe.c
+++ b/arch/tile/gxio/mpipe.c
@@ -19,6 +19,7 @@
 #include <linux/errno.h>
 #include <linux/io.h>
 #include <linux/module.h>
+#include <linux/string.h>
 
 #include <gxio/iorpc_globals.h>
 #include <gxio/iorpc_mpipe.h>
@@ -29,32 +30,6 @@
 /* HACK: Avoid pointless "shadow" warnings. */
 #define link link_shadow
 
-/**
- * strscpy - Copy a C-string into a sized buffer, but only if it fits
- * @dest: Where to copy the string to
- * @src: Where to copy the string from
- * @size: size of destination buffer
- *
- * Use this routine to avoid copying too-long strings.
- * The routine returns the total number of bytes copied
- * (including the trailing NUL) or zero if the buffer wasn't
- * big enough.  To ensure that programmers pay attention
- * to the return code, the destination has a single NUL
- * written at the front (if size is non-zero) when the
- * buffer is not big enough.
- */
-static size_t strscpy(char *dest, const char *src, size_t size)
-{
-	size_t len = strnlen(src, size) + 1;
-	if (len > size) {
-		if (size)
-			dest[0] = '\0';
-		return 0;
-	}
-	memcpy(dest, src, len);
-	return len;
-}
-
 int gxio_mpipe_init(gxio_mpipe_context_t *context, unsigned int mpipe_index)
 {
 	char file[32];
@@ -540,7 +515,7 @@ int gxio_mpipe_link_instance(const char *link_name)
 	if (!context)
 		return GXIO_ERR_NO_DEVICE;
 
-	if (strscpy(name.name, link_name, sizeof(name.name)) == 0)
+	if (strscpy(name.name, link_name, sizeof(name.name)) < 0)
 		return GXIO_ERR_NO_DEVICE;
 
 	return gxio_mpipe_info_instance_aux(context, name);
@@ -559,7 +534,7 @@ int gxio_mpipe_link_enumerate_mac(int idx, char *link_name, uint8_t *link_mac)
 
 	rv = gxio_mpipe_info_enumerate_aux(context, idx, &name, &mac);
 	if (rv >= 0) {
-		if (strscpy(link_name, name.name, sizeof(name.name)) == 0)
+		if (strscpy(link_name, name.name, sizeof(name.name)) < 0)
 			return GXIO_ERR_INVAL_MEMORY_SIZE;
 		memcpy(link_mac, mac.mac, sizeof(mac.mac));
 	}
@@ -576,7 +551,7 @@ int gxio_mpipe_link_open(gxio_mpipe_link_t *link,
 	_gxio_mpipe_link_name_t name;
 	int rv;
 
-	if (strscpy(name.name, link_name, sizeof(name.name)) == 0)
+	if (strscpy(name.name, link_name, sizeof(name.name)) < 0)
 		return GXIO_ERR_NO_DEVICE;
 
 	rv = gxio_mpipe_link_open_aux(context, name, flags);