[RFC PATCH 1/1] patch: fix seg fault caused by malformed patch

[Jim Keniston]

busybox's patch command dies with a SIGSEGV if the "---" line that heralds
a new file to patch is missing.  GNU patch silently does what's apparently
wanted, based on the "+++" line.

Signed-off-by: Jim Keniston <jkenisto at linux.vnet.ibm.com>

diff -up ./editors/patch.c.orig ./editors/patch.c
--- ./editors/patch.c.orig	2015-02-25 18:28:29.231096889 -0600
+++ ./editors/patch.c	2015-02-26 16:21:23.560131205 -0600
@@ -345,6 +345,8 @@ done:
 // state 1: Found +++ file indicator, look for @@
 // state 2: In hunk: counting initial context lines
 // state 3: In hunk: getting body
+// Like GNU patch, we don't require a --- line before the +++, and
+// also allow the --- after the +++ line.
 
 int patch_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int patch_main(int argc UNUSED_PARAM, char **argv)
@@ -462,6 +464,14 @@ int patch_main(int argc UNUSED_PARAM, ch
 			TT.context = 0;
 			state = 2;
 
+			// If the --- line is missing or malformed, either oldname
+			// or (for -R) newname could be NULL -- but not both.  Like
+			// GNU patch, proceed based on the +++ line, and avoid SEGVs.
+			if (!oldname)
+				oldname = xstrdup(newname);
+			else if (!newname)
+				newname = xstrdup(oldname);
+
 			// If this is the first hunk, open the file.
 			if (TT.filein == -1) {
 				int oldsum, newsum, empty = 0;