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Commit1db12da

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Fix unaligned memory access in xlog parsing due to replication origin patch.
ParseCommitRecord() accessed xl_xact_origin directly. But the chunks inthe commit record's data only have 4 byte alignment, whereasxl_xact_origin's members require 8 byte alignment on someplatforms. Update comments to make not of that and copy the record tostack local storage before reading.With help from Stefan Kaltenbrunner in pinning down the buildfarm andverifying the fix.
1 parent484a848 commit1db12da

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2 files changed

+9
-5
lines changed

2 files changed

+9
-5
lines changed

‎src/backend/access/rmgrdesc/xactdesc.c

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -104,10 +104,13 @@ ParseCommitRecord(uint8 info, xl_xact_commit *xlrec, xl_xact_parsed_commit *pars
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105105
if (parsed->xinfo&XACT_XINFO_HAS_ORIGIN)
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{
107-
xl_xact_origin*xl_origin= (xl_xact_origin*)data;
107+
xl_xact_originxl_origin;
108108

109-
parsed->origin_lsn=xl_origin->origin_lsn;
110-
parsed->origin_timestamp=xl_origin->origin_timestamp;
109+
/* we're only guaranteed 4 byte alignment, so copy onto stack */
110+
memcpy(&xl_origin,data,sizeof(xl_origin));
111+
112+
parsed->origin_lsn=xl_origin.origin_lsn;
113+
parsed->origin_timestamp=xl_origin.origin_timestamp;
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112115
data+=sizeof(xl_xact_origin);
113116
}

‎src/include/access/xact.h

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -173,7 +173,8 @@ typedef struct xl_xact_assignment
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* by a set XLOG_XACT_HAS_INFO bit in the xl_info field.
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*
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* NB: All the individual data chunks should be sized to multiples of
176-
* sizeof(int) and only require int32 alignment.
176+
* sizeof(int) and only require int32 alignment. If they require bigger
177+
* alignment, they need to be copied upon reading.
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*/
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/* sub-records for commit/abort */
@@ -237,7 +238,7 @@ typedef struct xl_xact_commit
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/* xl_xact_relfilenodes follows if XINFO_HAS_RELFILENODES */
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/* xl_xact_invals follows if XINFO_HAS_INVALS */
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/* xl_xact_twophase follows if XINFO_HAS_TWOPHASE */
240-
/* xl_xact_origin follows if XINFO_HAS_ORIGIN */
241+
/* xl_xact_origin follows if XINFO_HAS_ORIGIN, stored unaligned! */
241242
}xl_xact_commit;
242243
#defineMinSizeOfXactCommit (offsetof(xl_xact_commit, xact_time) + sizeof(TimestampTz))
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