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authorTom Lane <tgl@sss.pgh.pa.us>2025-01-30 15:36:07 -0500
committerTom Lane <tgl@sss.pgh.pa.us>2025-01-30 15:36:07 -0500
commitb296e55b4272494c54a7a65bec99d60200480051 (patch)
tree957307ac0c5ca27798264357dbfd51fe1bea492f /src/fe_utils/string_utils.c
parentbb85d09355832e8249b1af40fd181b6e791d87b5 (diff)
downloadpostgresql-b296e55b4272494c54a7a65bec99d60200480051.tar.gz
postgresql-b296e55b4272494c54a7a65bec99d60200480051.zip
Avoid integer overflow while testing wal_skip_threshold condition.
smgrDoPendingSyncs had two distinct risks of integer overflow while deciding which way to ensure durability of a newly-created relation. First, it accumulated the total size of all forks in a variable of type BlockNumber (uint32). While we restrict an individual fork's size to fit in that, I don't believe there's such a restriction on all of them added together. Second, it proceeded to multiply the sum by BLCKSZ, which most certainly could overflow a uint32. (The exact expression is total_blocks * BLCKSZ / 1024. The compiler might choose to optimize that to total_blocks * 8, which is not at quite as much risk of overflow as a literal reading would be, but it's still wrong.) If an overflow did occur it could lead to a poor choice to shove a very large relation into WAL instead of fsync'ing it. This wouldn't be fatal, but it could be inefficient. Change total_blocks to uint64 which should be plenty, and rearrange the comparison calculation to be overflow-safe. I noticed this while looking for ramifications of the proposed change in MAX_KILOBYTES. It's not entirely clear to me why wal_skip_threshold is limited to MAX_KILOBYTES in the first place, but in any case this code is unsafe regardless of the range of wal_skip_threshold. Oversight in c6b92041d which introduced wal_skip_threshold, so back-patch to v13. Discussion: https://postgr.es/m/1a01f0-66ec2d80-3b-68487680@27595217 Backpatch-through: 13
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