From: Konstantin Ovsepian ovs@ovs.to
[ Upstream commit 9bce8005ec0dcb23a58300e8522fe4a31da606fa ]
Recently running UBSAN caught few out of bound shifts in the ioc_forgive_debts() function:
UBSAN: shift-out-of-bounds in block/blk-iocost.c:2142:38 shift exponent 80 is too large for 64-bit type 'u64' (aka 'unsigned long long') ... UBSAN: shift-out-of-bounds in block/blk-iocost.c:2144:30 shift exponent 80 is too large for 64-bit type 'u64' (aka 'unsigned long long') ... Call Trace: <IRQ> dump_stack_lvl+0xca/0x130 __ubsan_handle_shift_out_of_bounds+0x22c/0x280 ? __lock_acquire+0x6441/0x7c10 ioc_timer_fn+0x6cec/0x7750 ? blk_iocost_init+0x720/0x720 ? call_timer_fn+0x5d/0x470 call_timer_fn+0xfa/0x470 ? blk_iocost_init+0x720/0x720 __run_timer_base+0x519/0x700 ...
Actual impact of this issue was not identified but I propose to fix the undefined behaviour. The proposed fix to prevent those out of bound shifts consist of precalculating exponent before using it the shift operations by taking min value from the actual exponent and maximum possible number of bits.
Reported-by: Breno Leitao leitao@debian.org Signed-off-by: Konstantin Ovsepian ovs@ovs.to Acked-by: Tejun Heo tj@kernel.org Link: https://lore.kernel.org/r/20240822154137.2627818-1-ovs@ovs.to Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-iocost.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c index 0dca77591d66c..c3cb9c20b306c 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -2076,7 +2076,7 @@ static void ioc_forgive_debts(struct ioc *ioc, u64 usage_us_sum, int nr_debtors, struct ioc_now *now) { struct ioc_gq *iocg; - u64 dur, usage_pct, nr_cycles; + u64 dur, usage_pct, nr_cycles, nr_cycles_shift;
/* if no debtor, reset the cycle */ if (!nr_debtors) { @@ -2138,10 +2138,12 @@ static void ioc_forgive_debts(struct ioc *ioc, u64 usage_us_sum, int nr_debtors, old_debt = iocg->abs_vdebt; old_delay = iocg->delay;
+ nr_cycles_shift = min_t(u64, nr_cycles, BITS_PER_LONG - 1); if (iocg->abs_vdebt) - iocg->abs_vdebt = iocg->abs_vdebt >> nr_cycles ?: 1; + iocg->abs_vdebt = iocg->abs_vdebt >> nr_cycles_shift ?: 1; + if (iocg->delay) - iocg->delay = iocg->delay >> nr_cycles ?: 1; + iocg->delay = iocg->delay >> nr_cycles_shift ?: 1;
iocg_kick_waitq(iocg, true, now);