Fix out-of-bounds access in autoprewarm worker The read stream callback apw_read_stream_next_block() advances p->pos through the block_info array. When processing the last block, it increments p->pos to prewarm_stop_idx before returning. The callback itself is safe because it checks bounds before accessing the array.
However, the caller assigned blk from block_info[i] at the end of the loop body, before the loop condition was re-evaluated. When i equaled prewarm_stop_idx, this accessed memory beyond the allocated DSM segment, causing a segfault. Restructure the loop to check bounds at the top and assign blk at the beginning of the loop body, where it is always safe. This avoids the need for an explicit bounds check at the end. Backpatch to 18, where the bug was introduced by commit 6acab8bdbcda. Author: Matheus Alcantara <[email protected]> Reported-by: Glauber Batista <[email protected]> Reviewed-by: Melanie Plageman <[email protected]> Reviewed-by: Tomas Vondra <[email protected]> Backpatch-through: 18 Discussion: https://www.postgresql.org/message-id/CAO%2B_mTQgQyTYwDh%3DU8iTnsDmOGyWsZJjUV31SmEYwmw6_xY6Bw%40mail.gmail.com Branch ------ REL_18_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/3bf2cb22576eac50d80e3eecd485fcae4fdd7f8b Modified Files -------------- contrib/pg_prewarm/autoprewarm.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-)
