From: drh <drh@noemail.net>
Date: Fri, 21 May 2010 13:16:18 +0000 (+0000)
Subject: Fix the wal-index header read routine so that it correctly detects a zero
X-Git-Tag: version-3.7.2~354
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f0b20f8801e1a2e203aa26104cddaf522f935145;p=thirdparty%2Fsqlite.git

Fix the wal-index header read routine so that it correctly detects a zero
header as being malformed and in need of a wal-index rebuild.

FossilOrigin-Name: 1a4eb3a3efe86c7caff4d9a5894953bce378f841
---

diff --git a/manifest b/manifest
index 4b9430e5b6..5a581f39da 100644
--- a/manifest
+++ b/manifest
@@ -1,8 +1,8 @@
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
-C Add\sa\snew\sxShmBarrier\smethod\sto\sthe\sVFS\s-\sa\sshared-memory\sfence\soperation.\nImplement\sthe\ssame\sin\sboth\sunix\sand\swin32.\s\sUse\sit\sto\smake\sthe\sWAL\ssubsystem\nmore\srobust.
-D 2010-05-20T23:51:07
+C Fix\sthe\swal-index\sheader\sread\sroutine\sso\sthat\sit\scorrectly\sdetects\sa\szero\nheader\sas\sbeing\smalformed\sand\sin\sneed\sof\sa\swal-index\srebuild.
+D 2010-05-21T13:16:19
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in a5cad1f8f3e021356bfcc6c77dc16f6f1952bbc3
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -227,7 +227,7 @@ F src/vdbeblob.c 5327132a42a91e8b7acfb60b9d2c3b1c5c863e0e
 F src/vdbemem.c 2a82f455f6ca6f78b59fb312f96054c04ae0ead1
 F src/vdbetrace.c 864cef96919323482ebd9986f2132435115e9cc2
 F src/vtab.c a0f8a40274e4261696ef57aa806de2776ab72cda
-F src/wal.c 2352dd3a2bb271e5c76c9c4407f6590ae5e3768c
+F src/wal.c 1c3abceacad9659ecd1558be75a2114d953d3b7e
 F src/wal.h 434f76f51225bb614e43ccb6bd2341541ba6a06e
 F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
 F src/where.c 75fee9e255b62f773fcadd1d1f25b6f63ac7a356
@@ -816,14 +816,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P 9580ecb7e3beb1949a71784a3dcd1823a88e4a9d
-R 6169e39cb99c7a86e9c9e7505a7068ac
+P 1bd011c9fed5ef29fb616b4d0a52df3b82221b1f
+R b1aca10baf167dbb95ab7e54f5a950e6
 U drh
-Z b1a49e07405386f7203bad3d085615ae
+Z 69b1bc82a1680c243dd4a43f4faa2d67
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1.4.6 (GNU/Linux)
 
-iD8DBQFL9cruoxKgR168RlERAkAFAJ9xRzU75gC9SA4GXt3kPWkhCqvfpACdF9xG
-lxuM43sIwrUxctG6rY11InI=
-=HHWB
+iD8DBQFL9oenoxKgR168RlERAhg+AJ9n9qywdfuiNJpDkY+WtSlKP+eZVgCffwF8
+SmDbNBLJmDSM4k/xfAbThXY=
+=j0sy
 -----END PGP SIGNATURE-----
diff --git a/manifest.uuid b/manifest.uuid
index 767cd5e0f2..b7c453becd 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-1bd011c9fed5ef29fb616b4d0a52df3b82221b1f
\ No newline at end of file
+1a4eb3a3efe86c7caff4d9a5894953bce378f841
\ No newline at end of file
diff --git a/src/wal.c b/src/wal.c
index 65c711d8f1..a320d25e99 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -1126,7 +1126,7 @@ int sqlite3WalClose(
 */
 int walIndexTryHdr(Wal *pWal, int *pChanged){
   u32 aCksum[2];               /* Checksum on the header content */
-  WalIndexHdr hdr1, hdr2;      /* Two copies of the header content */
+  WalIndexHdr h1, h2;          /* Two copies of the header content */
   WalIndexHdr *aHdr;           /* Header in shared memory */
 
   assert( pWal->pWiData );
@@ -1142,25 +1142,31 @@ int walIndexTryHdr(Wal *pWal, int *pChanged){
   ** (WRITE, PENDING, CHECKPOINT or RECOVER) lock on the wal-index
   ** file, meaning it is possible that an inconsistent snapshot is read
   ** from the file. If this happens, return non-zero.
+  **
+  ** There are two copies of the header at the beginning of the wal-index.
+  ** When reading, read [0] first then [1].  Writes are in the reverse order.
+  ** Memory barriers are used to prevent the compiler or the hardware from
+  ** reordering the reads and writes.
   */
   aHdr = (WalIndexHdr*)pWal->pWiData;
-  memcpy(&hdr1, &aHdr[0], sizeof(hdr1));
+  memcpy(&h1, &aHdr[0], sizeof(h1));
   sqlite3OsShmBarrier(pWal->pDbFd);
-  memcpy(&hdr2, &aHdr[1], sizeof(hdr2));
+  memcpy(&h2, &aHdr[1], sizeof(h2));
 
-  if( memcmp(&hdr1, &hdr2, sizeof(hdr1))!=0 ){
-    /* Dirty read */
-    return 1;
+  if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
+    return 1;   /* Dirty read */
   }  
-  walChecksumBytes((u8*)&hdr1, sizeof(hdr1)-sizeof(hdr1.aCksum), 0, aCksum);
-  if( aCksum[0]!=hdr1.aCksum[0] || aCksum[1]!=hdr1.aCksum[1] ){
-    /* Malformed header */
-    return 1;
+  if( h1.szPage==0 ){
+    return 1;   /* Malformed header - probably all zeros */
+  }
+  walChecksumBytes((u8*)&h1, sizeof(h1)-sizeof(h1.aCksum), 0, aCksum);
+  if( aCksum[0]!=h1.aCksum[0] || aCksum[1]!=h1.aCksum[1] ){
+    return 1;   /* Checksum does not match */
   }
 
-  if( memcmp(&pWal->hdr, &hdr1, sizeof(WalIndexHdr)) ){
+  if( memcmp(&pWal->hdr, &h1, sizeof(WalIndexHdr)) ){
     *pChanged = 1;
-    memcpy(&pWal->hdr, &hdr1, sizeof(WalIndexHdr));
+    memcpy(&pWal->hdr, &h1, sizeof(WalIndexHdr));
     pWal->szPage = pWal->hdr.szPage;
   }