From 0730dd4ffb39358f30b1a956cd9182aed1958b47 Mon Sep 17 00:00:00 2001
From: Jeff King <peff@peff.net>
Date: Thu, 30 Mar 2017 06:35:50 -0400
Subject: difftool: avoid strcpy

In order to checkout files, difftool reads "diff --raw"
output and feeds the names to checkout_entry(). That
function requires us to have a "struct cache_entry". And
because that struct uses a FLEX_ARRAY for the name field, we
have to actually copy in our new name.

The current code allocates a single re-usable cache_entry
that can hold a name up to PATH_MAX, and then copies
filenames into it using strcpy(). But there's no guarantee
that incoming names are smaller than PATH_MAX. They've come
from "diff --raw" output which might be diffing between two
trees (and hence we'd be subject to the PATH_MAX of some
other system, or even none at all if they were created
directly via "update-index").

We can fix this by using make_cache_entry() to create a
correctly-sized cache_entry for each name. This incurs an
extra allocation per file, but this is negligible compared
to actually writing out the file contents.

To make this simpler, we can push this procedure into a new
helper function. Note that we can also get rid of the "len"
variables for src_path and dst_path (and in fact we must, as
the compiler complains that they are unused).

Signed-off-by: Jeff King <peff@peff.net>
Acked-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/difftool.c b/builtin/difftool.c
index 25e54ad..b350b3d 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -297,6 +297,19 @@ static char *get_symlink(const struct object_id *oid, const char *path)
 	return data;
 }
 
+static int checkout_path(unsigned mode, struct object_id *oid,
+			 const char *path, const struct checkout *state)
+{
+	struct cache_entry *ce;
+	int ret;
+
+	ce = make_cache_entry(mode, oid->hash, path, 0, 0);
+	ret = checkout_entry(ce, state, NULL);
+
+	free(ce);
+	return ret;
+}
+
 static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 			int argc, const char **argv)
 {
@@ -306,7 +319,6 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 	struct strbuf ldir = STRBUF_INIT, rdir = STRBUF_INIT;
 	struct strbuf wtdir = STRBUF_INIT;
 	size_t ldir_len, rdir_len, wtdir_len;
-	struct cache_entry *ce = xcalloc(1, sizeof(ce) + PATH_MAX + 1);
 	const char *workdir, *tmp;
 	int ret = 0, i;
 	FILE *fp;
@@ -377,7 +389,6 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 		struct object_id loid, roid;
 		char status;
 		const char *src_path, *dst_path;
-		size_t src_path_len, dst_path_len;
 
 		if (starts_with(info.buf, "::"))
 			die(N_("combined diff formats('-c' and '--cc') are "
@@ -390,17 +401,14 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 		if (strbuf_getline_nul(&lpath, fp))
 			break;
 		src_path = lpath.buf;
-		src_path_len = lpath.len;
 
 		i++;
 		if (status != 'C' && status != 'R') {
 			dst_path = src_path;
-			dst_path_len = src_path_len;
 		} else {
 			if (strbuf_getline_nul(&rpath, fp))
 				break;
 			dst_path = rpath.buf;
-			dst_path_len = rpath.len;
 		}
 
 		if (S_ISGITLINK(lmode) || S_ISGITLINK(rmode)) {
@@ -430,11 +438,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 		}
 
 		if (lmode && status != 'C') {
-			ce->ce_mode = lmode;
-			oidcpy(&ce->oid, &loid);
-			strcpy(ce->name, src_path);
-			ce->ce_namelen = src_path_len;
-			if (checkout_entry(ce, &lstate, NULL))
+			if (checkout_path(lmode, &loid, src_path, &lstate))
 				return error("could not write '%s'", src_path);
 		}
 
@@ -451,11 +455,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 			hashmap_add(&working_tree_dups, entry);
 
 			if (!use_wt_file(workdir, dst_path, &roid)) {
-				ce->ce_mode = rmode;
-				oidcpy(&ce->oid, &roid);
-				strcpy(ce->name, dst_path);
-				ce->ce_namelen = dst_path_len;
-				if (checkout_entry(ce, &rstate, NULL))
+				if (checkout_path(rmode, &roid, dst_path, &rstate))
 					return error("could not write '%s'",
 						     dst_path);
 			} else if (!is_null_oid(&roid)) {
@@ -625,7 +625,6 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 		exit_cleanup(tmpdir, rc);
 
 finish:
-	free(ce);
 	strbuf_release(&ldir);
 	strbuf_release(&rdir);
 	strbuf_release(&wtdir);
-- 
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