[sql] Rewrite sqlite patching "system".

third_party/sqlite/patches/0015-fts3-Interior-node-corruption-detection.patch

+From 791a4ecc9e9f325c9eab9d6e6b478fe7533b3edd Mon Sep 17 00:00:00 2001
+From: Scott Hess <shess@chromium.org>
+Date: Tue, 23 Dec 2014 13:23:08 -0800
+Subject: [PATCH 15/24] [fts3] Interior node corruption detection.
+
+In auditing as part of a previous import, I noticed this case which
+seemed to allow for buffer overrun.  The nPrefix check was commented out
+because nBuffer wasn't always initialized, and I never circled back to
+resolve that.
+
+It may be appropriate to just drop this patch, for now leaving it for
+consistency.
+
+BUG=84057, 83946
+---
+ third_party/sqlite/src/ext/fts3/fts3.c | 8 +++++++-
+ 1 file changed, 7 insertions(+), 1 deletion(-)
+
+diff --git a/third_party/sqlite/src/ext/fts3/fts3.c b/third_party/sqlite/src/ext/fts3/fts3.c
+index da55f2a..d11572a 100644
+--- a/third_party/sqlite/src/ext/fts3/fts3.c
++++ b/third_party/sqlite/src/ext/fts3/fts3.c
+@@ -1230,7 +1230,13 @@ static int fts3ScanInteriorNode(
+     isFirstTerm = 0;
+     zCsr += sqlite3Fts3GetVarint32(zCsr, &nSuffix);
+     
+-    if( nPrefix<0 || nSuffix<0 || &zCsr[nSuffix]>zEnd ){
++    /* NOTE(shess): Previous code checked for negative nPrefix and
++    ** nSuffix and suffix overrunning zEnd.  Additionally corrupt if
++    ** the prefix is longer than the previous term, or if the suffix
++    ** causes overflow.
++    */
++    if( nPrefix<0 || nSuffix<0 /* || nPrefix>nBuffer */
++     || &zCsr[nSuffix]<zCsr || &zCsr[nSuffix]>zEnd ){
+       rc = SQLITE_CORRUPT;
+       goto finish_scan;
+     }
+-- 
+2.2.1
+