If the filename argument to sqlite3_load_extension() is an empty string, then

raise an error.  It turns out that if dlopen() is called with an empty
filename, it tries to load the current executable.  And then if the caller
requests some other function from the current executable, mischief can result.

FossilOrigin-Name: d01688554715eb4aaa1b1fd1a6b660b84e930edb0e062156ecf5228ee81ca754

manifest

@@ -1,5 +1,5 @@
-C Add\san\sALWAYS()\son\san\sunreachable\sbranch.
-D 2023-06-01T00:28:11.164
+C If\sthe\sfilename\sargument\sto\ssqlite3_load_extension()\sis\san\sempty\sstring,\sthen\nraise\san\serror.\s\sIt\sturns\sout\sthat\sif\sdlopen()\sis\scalled\swith\san\sempty\nfilename,\sit\stries\sto\sload\sthe\scurrent\sexecutable.\s\sAnd\sthen\sif\sthe\scaller\nrequests\ssome\sother\sfunction\sfrom\sthe\scurrent\sexecutable,\smischief\scan\sresult.
+D 2023-06-01T16:40:28.030
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -599,7 +599,7 @@ F src/in-operator.md 10cd8f4bcd225a32518407c2fb2484089112fd71
 F src/insert.c a8de1db43335fc4946370a7a7e47d89975ad678ddb15078a150e993ba2fb37d4
 F src/json.c 39b1c7527f3111923e65f168a87b03b591f12a41400a63d05c119794bee36620
 F src/legacy.c d7874bc885906868cd51e6c2156698f2754f02d9eee1bae2d687323c3ca8e5aa
-F src/loadext.c be5af440f3192c58681b5d43167dbca3ccbfce394d89faa22378a14264781136
+F src/loadext.c 176d6b2cb18a6ad73b133db17f6fc351c4d9a2d510deebdb76c22bde9cfd1465
 F src/main.c 035be2e9ba2a0fc1701a8ab1880af3001a968a24556433538a6c073558ee4341
 F src/malloc.c 47b82c5daad557d9b963e3873e99c22570fb470719082c6658bf64e3012f7d23
 F src/mem0.c 6a55ebe57c46ca1a7d98da93aaa07f99f1059645
@@ -2072,8 +2072,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 96c72dde79d4069f6c2f81467a35b617633f86f7a7dcafbda991affdaa1f8537
-R 40ac9a38209c3dcd8c11c72579ce41b0
+P a00928d48061c1169d5564996e19e7d7c2b962842100bb119846d0f696123c23
+R c8967c78f434ef2509738e62135df025
 U drh
-Z 6c162dfd8f6d4fb3cc66b56b381f7dc7
+Z 1cc3ad466999e676142d799de6799c56
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-a00928d48061c1169d5564996e19e7d7c2b962842100bb119846d0f696123c23
+d01688554715eb4aaa1b1fd1a6b660b84e930edb0e062156ecf5228ee81ca754

src/loadext.c

@@ -591,6 +591,10 @@ static int sqlite3LoadExtension(
   ** See https://sqlite.org/forum/forumpost/24083b579d.
   */
   if( nMsg>SQLITE_MAX_PATHLEN ) goto extension_not_found;
+
+  /* Do not allow sqlite3_load_extension() to link to a copy of the
+  ** running application, by passing in an empty filename. */
+  if( nMsg==0 ) goto extension_not_found;
     
   handle = sqlite3OsDlOpen(pVfs, zFile);
 #if SQLITE_OS_UNIX || SQLITE_OS_WIN