Ensure all bytes of the PgHdr1 structure are initialized. This avoids a valgrind error when running corruptI.test.

FossilOrigin-Name: a505e34d4ec31159a4508ec827fcffed0cf3bd5ea5ef0ac293016da02367a53a

1 files changed, 13 insertions, 2 deletions

diff --git a/src/pcache1.c b/src/pcache1.c
index 72e81bb2b..5f502d57b 100644
--- a/src/pcache1.c
+++ b/src/pcache1.c
@@ -92,12 +92,22 @@ typedef struct PGroup PGroup;
 ** structure. Unless SQLITE_PCACHE_SEPARATE_HEADER is defined, a buffer of
 ** PgHdr1.pCache->szPage bytes is allocated directly before this structure 
 ** in memory.
+**
+** Note: Variables isBulkLocal and isAnchor were once type "u8". That works,
+** but causes a 2-byte gap in the structure for most architectures (since 
+** pointers must be either 4 or 8-byte aligned). As this structure is located
+** in memory directly after the associated page data, if the database is
+** corrupt, code at the b-tree layer may overread the page buffer and 
+** read part of this structure before the corruption is detected. This
+** can cause a valgrind error if the unitialized gap is accessed. Using u16
+** ensures there is no such gap, and therefore no bytes of unitialized memory
+** in the structure.
 */
 struct PgHdr1 {
   sqlite3_pcache_page page;      /* Base class. Must be first. pBuf & pExtra */
   unsigned int iKey;             /* Key value (page number) */
-  u8 isBulkLocal;                /* This page from bulk local storage */
-  u8 isAnchor;                   /* This is the PGroup.lru element */
+  u16 isBulkLocal;               /* This page from bulk local storage */
+  u16 isAnchor;                  /* This is the PGroup.lru element */
   PgHdr1 *pNext;                 /* Next in hash table chain */
   PCache1 *pCache;               /* Cache that currently owns this page */
   PgHdr1 *pLruNext;              /* Next in LRU list of unpinned pages */
@@ -303,6 +313,7 @@ static int pcache1InitBulk(PCache1 *pCache){
       pX->isBulkLocal = 1;
       pX->isAnchor = 0;
       pX->pNext = pCache->pFree;
+      pX->pLruPrev = 0;           /* Initializing this saves a valgrind error */
       pCache->pFree = pX;
       zBulk += pCache->szAlloc;
     }while( --nBulk );