blk-throttle: check for overflow in calculate_bytes_allowed

commit 2dd710d upstream. Inexact, we may reject some not-overflowing values incorrectly, but they'll be on the order of exabytes allowed anyways. This fixes divide error crash on x86 if bps_limit is not configured or is set too high in the rare case that jiffy_elapsed is greater than HZ. Fixes: e8368b5 ("blk-throttle: use calculate_io/bytes_allowed() for throtl_trim_slice()") Fixes: 8d6bbaa ("blk-throttle: prevent overflow while calculating wait time") Signed-off-by: Khazhismel Kumykov <[email protected]> Acked-by: Tejun Heo <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Jens Axboe <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
raspberrypi · Nov 2, 2023 · 6cf9373 · 6cf9373
1 parent c031d9a
commit 6cf9373
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
@@ -723,6 +723,12 @@ static unsigned int calculate_io_allowed(u32 iops_limit,
 
 static u64 calculate_bytes_allowed(u64 bps_limit, unsigned long jiffy_elapsed)
 {
+	/*
+	 * Can result be wider than 64 bits?
+	 * We check against 62, not 64, due to ilog2 truncation.
+	 */
+	if (ilog2(bps_limit) + ilog2(jiffy_elapsed) - ilog2(HZ) > 62)
+		return U64_MAX;
 	return mul_u64_u64_div_u64(bps_limit, (u64)jiffy_elapsed, (u64)HZ);
 }