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Fix potential stack overflow in incremental backup.

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The user can set RELSEG_SIZE to a high number at compile time, so we
can't use it to control the size of an array on the stack: it could be
many gigabytes in size.  On closer inspection, we don't really need that
intermediate array anyway.  Let's just write directly into the output
array, and then perform the absolute->relative adjustment in place.
This fixes new code from commit dc212340058.

Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKG%2B2hZ0sBztPW4mkLfng0qfkNtAHFUfxOMLizJ0BPmi5%2Bg%40mail.gmail.com
This commit is contained in:
Thomas Munro 2024-04-11 13:19:29 +12:00
parent f56a9def71
commit d8f5acbdb9
1 changed files with 17 additions and 9 deletions
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26
src/backend/backup/basebackup_incremental.c
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@ -726,7 +726,8 @@ GetIncrementalFilePath(Oid dboid, Oid spcoid, RelFileNumber relfilenumber,
* How should we back up a particular file as part of an incremental backup?
*
* If the return value is BACK_UP_FILE_FULLY, caller should back up the whole
* file just as if this were not an incremental backup.
* file just as if this were not an incremental backup. The contents of the
* relative_block_numbers array is unspecified in this case.
*
* If the return value is BACK_UP_FILE_INCREMENTALLY, caller should include
* an incremental file in the backup instead of the entire file. On return,
@ -745,7 +746,6 @@ GetFileBackupMethod(IncrementalBackupInfo *ib, const char *path,
BlockNumber *relative_block_numbers,
unsigned *truncation_block_length)
{
BlockNumber absolute_block_numbers[RELSEG_SIZE];
BlockNumber limit_block;
BlockNumber start_blkno;
BlockNumber stop_blkno;
@ -872,8 +872,13 @@ GetFileBackupMethod(IncrementalBackupInfo *ib, const char *path,
errcode(ERRCODE_INTERNAL_ERROR),
errmsg_internal("overflow computing block number bounds for segment %u with size %zu",
segno, size));
/*
* This will write *absolute* block numbers into the output array, but
* we'll transpose them below.
*/
nblocks = BlockRefTableEntryGetBlocks(brtentry, start_blkno, stop_blkno,
absolute_block_numbers, RELSEG_SIZE);
relative_block_numbers, RELSEG_SIZE);
Assert(nblocks <= RELSEG_SIZE);
/*
@ -892,19 +897,22 @@ GetFileBackupMethod(IncrementalBackupInfo *ib, const char *path,
return BACK_UP_FILE_FULLY;
/*
* Looks like we can send an incremental file, so sort the absolute the
* block numbers and then transpose absolute block numbers to relative
* block numbers.
* Looks like we can send an incremental file, so sort the block numbers
* and then transpose them from absolute block numbers to relative block
* numbers if necessary.
*
* NB: If the block reference table was using the bitmap representation
* for a given chunk, the block numbers in that chunk will already be
* sorted, but when the array-of-offsets representation is used, we can
* receive block numbers here out of order.
*/
qsort(absolute_block_numbers, nblocks, sizeof(BlockNumber),
qsort(relative_block_numbers, nblocks, sizeof(BlockNumber),
compare_block_numbers);
for (i = 0; i < nblocks; ++i)
relative_block_numbers[i] = absolute_block_numbers[i] - start_blkno;
if (start_blkno != 0)
{
for (i = 0; i < nblocks; ++i)
relative_block_numbers[i] -= start_blkno;
}
*num_blocks_required = nblocks;
/*