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Fix the wal-index header read routine so that it correctly detects a zero

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header as being malformed and in need of a wal-index rebuild.

FossilOrigin-Name: 1a4eb3a3efe86c7caff4d9a5894953bce378f841
This commit is contained in:
drh
2010-05-21 13:16:18 +00:00
parent 286a288493
commit f0b20f8801
3 changed files with 28 additions and 22 deletions
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30
src/wal.c
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@@ -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;
}