In os_unix.c and os_win.c, do not allow xFetch() to return a pointer to a page buffer that is right at the end of the mapped region - if the database is corrupted in a specific way such a page buffer might be overread by several bytes.

FossilOrigin-Name: 2684feac3bc9c5463604900d72710be861527614f4957224c74a16a3b3c702f5

manifest

@@ -1,5 +1,5 @@
-C Improved\serror\smessage\swhen\sa\sdouble-quoted\sidentifier\sname\scannot\sbe\nresolved\s-\sask\sthe\suser\sif\sthey\sintended\sto\suse\sa\sstring\sliteral.
-D 2024-01-23T14:45:22.468
+C In\sos_unix.c\sand\sos_win.c,\sdo\snot\sallow\sxFetch()\sto\sreturn\sa\spointer\sto\sa\spage\sbuffer\sthat\sis\sright\sat\sthe\send\sof\sthe\smapped\sregion\s-\sif\sthe\sdatabase\sis\scorrupted\sin\sa\sspecific\sway\ssuch\sa\spage\sbuffer\smight\sbe\soverread\sby\sseveral\sbytes.
+D 2024-01-23T16:09:22.291
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -722,8 +722,8 @@ F src/os.h 1ff5ae51d339d0e30d8a9d814f4b8f8e448169304d83a7ed9db66a65732f3e63
 F src/os_common.h 6c0eb8dd40ef3e12fe585a13e709710267a258e2c8dd1c40b1948a1d14582e06
 F src/os_kv.c 4d39e1f1c180b11162c6dc4aa8ad34053873a639bac6baae23272fc03349986a
 F src/os_setup.h 6011ad7af5db4e05155f385eb3a9b4470688de6f65d6166b8956e58a3d872107
-F src/os_unix.c 5dc41030cd5dfd99b907976b1725a4ed695566405d33744e4824c3d6aff245a3
-F src/os_win.c 4a50a154aeebc66a1f8fb79c1ff6dd5fe3d005556533361e0d460d41cb6a45a8
+F src/os_unix.c fa9b81b642e60e77ffaf98bd1a2e5fde16c1c2317614ec178bf3bd5864772356
+F src/os_win.c 6ff43bac175bd9ed79e7c0f96840b139f2f51d01689a638fd05128becf94908a
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c ff60e98138d2499082ac6230f01ac508aba545315debccfca2fd6042f5f10fcd
 F src/pager.h 4b1140d691860de0be1347474c51fee07d5420bd7f802d38cbab8ea4ab9f538a
@@ -1419,10 +1419,11 @@ F test/misc7.test d912f3d45c2989191b797504a220ca225d6be80b21acad22ba0d35f4a9ee45
 F test/misc8.test 4db9f8be59834cea08c87e9658014080efa02678ef54a088f84fa5647e81fee0
 F test/misuse.test 9e7f78402005e833af71dcab32d048003869eca5abcaccc985d4f8dc1d86bcc7
 F test/mjournal.test 28a08d5cb5fb5b5702a46e19176e45e964e0800d1f894677169e79f34030e152
-F test/mmap1.test 5c1f768828094b0dd94e55ae7f10489a1ded74772682be2c4c78679d0acaf7ef
+F test/mmap1.test e154d0442c9b43646f86b8ddc38b656bb8bc79284209a9367076473cec5d0eef
 F test/mmap2.test 9d6dd9ddb4ad2379f29cc78f38ce1e63ed418022
 F test/mmap3.test b3c297e78e6a8520aafcc1a8f140535594c9086e
 F test/mmap4.test 2e2b4e32555b58da15176e6fe750f17c9dcf7f93
+F test/mmapcorrupt.test 0d89724591f22a376019f3df60d075b838dd2ba6dae6effb0be465c49cf86d4a
 F test/mmapfault.test d4c9eff9cd8c2dc14bc43e71e042f175b0a26fe3
 F test/mmapwarm.test 2272005969cd17a910077bd5082f70bc1fefad9a875afec7fc9af483898ecaf3
 F test/multiplex.test d74c034e52805f6de8cc5432cef8c9eb774bb64ec29b83a22effc8ca4dac1f08
@@ -2160,9 +2161,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P e5dc81d5c7ee97866feb688dfa9b6fc225dabff2b020b9b96b49a8fea5640aec 59eb9d29e796886db17a578b64e75fd2797aebf969cbeeda70ecf2fda378c98f
-R c6b194554d1ef13c7fd9b0cfa6d21ae1
-T +closed 59eb9d29e796886db17a578b64e75fd2797aebf969cbeeda70ecf2fda378c98f
-U drh
-Z e1ae068dffaf45ea92f1b3624e579582
+P efc5c3c5e6ae1f9f0be61ea4ce7b3e34f3dc318791c78e0f4bebebeaccf6951e
+R d2fac210a7e93b5529ce586e57a37021
+U dan
+Z 75c6fc2c30c7c083cae329bbdba750e2
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-efc5c3c5e6ae1f9f0be61ea4ce7b3e34f3dc318791c78e0f4bebebeaccf6951e
+2684feac3bc9c5463604900d72710be861527614f4957224c74a16a3b3c702f5

src/os_unix.c

@@ -5441,11 +5441,16 @@ static int unixFetch(sqlite3_file *fd, i64 iOff, int nAmt, void **pp){
 
 #if SQLITE_MAX_MMAP_SIZE>0
   if( pFd->mmapSizeMax>0 ){
+    /* Ensure that there is always at least a 256 byte buffer of addressable
+    ** memory following the returned page. If the database is corrupt,
+    ** SQLite may overread the page slightly (in practice only a few bytes,
+    ** but 256 is safe, round, number).  */
+    const int nEofBuffer = 256;
     if( pFd->pMapRegion==0 ){
       int rc = unixMapfile(pFd, -1);
       if( rc!=SQLITE_OK ) return rc;
     }
-    if( pFd->mmapSize >= iOff+nAmt ){
+    if( pFd->mmapSize >= (iOff+nAmt+nEofBuffer) ){
       *pp = &((u8 *)pFd->pMapRegion)[iOff];
       pFd->nFetchOut++;
     }

src/os_win.c

@@ -4521,6 +4521,11 @@ static int winFetch(sqlite3_file *fd, i64 iOff, int nAmt, void **pp){
 
 #if SQLITE_MAX_MMAP_SIZE>0
   if( pFd->mmapSizeMax>0 ){
+    /* Ensure that there is always at least a 256 byte buffer of addressable
+    ** memory following the returned page. If the database is corrupt,
+    ** SQLite may overread the page slightly (in practice only a few bytes,
+    ** but 256 is safe, round, number).  */
+    const int nEofBuffer = 256;
     if( pFd->pMapRegion==0 ){
       int rc = winMapfile(pFd, -1);
       if( rc!=SQLITE_OK ){
@@ -4529,7 +4534,7 @@ static int winFetch(sqlite3_file *fd, i64 iOff, int nAmt, void **pp){
         return rc;
       }
     }
-    if( pFd->mmapSize >= iOff+nAmt ){
+    if( pFd->mmapSize >= (iOff+nAmt+nEofBuffer) ){
       assert( pFd->pMapRegion!=0 );
       *pp = &((u8 *)pFd->pMapRegion)[iOff];
       pFd->nFetchOut++;

test/mmap1.test

@@ -45,17 +45,17 @@ proc register_rblob_code {dbname seed} {
 }
 
 
-# For cases 1.1 and 1.4, the number of pages read using xRead() is 4 on
-# unix and 9 on windows. The difference is that windows only ever maps
+# For cases 1.1 and 1.4, the number of pages read using xRead() is 8 on
+# unix and 12 on windows. The difference is that windows only ever maps
 # an integer number of OS pages (i.e. creates mappings that are a multiple
 # of 4KB in size). Whereas on unix any sized mapping may be created.
 #
 foreach {t mmap_size nRead c2init} {
-  1.1 { PRAGMA mmap_size = 67108864 } /[49]/ {PRAGMA mmap_size = 0}
-  1.2 { PRAGMA mmap_size =    53248 } 150    {PRAGMA mmap_size = 0}
+  1.1 { PRAGMA mmap_size = 67108864 } /8|12/ {PRAGMA mmap_size = 0}
+  1.2 { PRAGMA mmap_size =    53248 } 154    {PRAGMA mmap_size = 0}
   1.3 { PRAGMA mmap_size =        0 } 344    {PRAGMA mmap_size = 0}
-  1.4 { PRAGMA mmap_size = 67108864 } /[49]/ {PRAGMA mmap_size = 67108864 }
-  1.5 { PRAGMA mmap_size =    53248 } 150    {PRAGMA mmap_size = 67108864 }
+  1.4 { PRAGMA mmap_size = 67108864 } /12|8/ {PRAGMA mmap_size = 67108864 }
+  1.5 { PRAGMA mmap_size =    53248 } 154    {PRAGMA mmap_size = 67108864 }
   1.6 { PRAGMA mmap_size =        0 } 344    {PRAGMA mmap_size = 67108864 }
 } {
 

test/mmapcorrupt.test

@@ -0,0 +1,51 @@
+# 2024 January 23
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+# Test special cases of corrupt database handling in mmap-mode.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix mmapcorrupt
+
+database_may_be_corrupt
+
+db close
+sqlite3_shutdown
+sqlite3_config_lookaside 0 0
+sqlite3_initialize
+
+reset_db
+do_execsql_test 1.0 {
+  PRAGMA page_size = 16384;
+  CREATE TABLE tn1(a PRIMARY KEY) WITHOUT ROWID;
+  CREATE TABLE t0(a PRIMARY KEY) WITHOUT ROWID;
+  CREATE TABLE t1(a PRIMARY KEY) WITHOUT ROWID;
+  INSERT INTO t1 VALUES('B');
+}
+db close
+
+set sz [file size test.db]
+hexio_write test.db [expr $sz-3] 800380
+
+sqlite3 db test.db
+do_execsql_test 2.1 {
+  PRAGMA mmap_size = 1000000;
+  SELECT sql FROM sqlite_schema LIMIT 1;
+  SELECT * FROM t0;
+} {1000000 {CREATE TABLE tn1(a PRIMARY KEY) WITHOUT ROWID}}
+
+do_execsql_test 2.2 {
+  INSERT INTO t0 SELECT * FROM t1;
+}
+
+finish_test
+