[PATCH] blk_iocost: fix more out of bound shifts

[PATCH] blk_iocost: fix more out of bound shifts

[Konstantin Ovsepian]

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>
---
 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 690ca99dfaca..5a6098a3db57 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);
 
-- 
2.43.5

Re: [PATCH] blk_iocost: fix more out of bound shifts

[Tejun Heo]

On Thu, Aug 22, 2024 at 08:41:36AM -0700, Konstantin Ovsepian wrote:
> 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>

Thanks.

-- 
tejun

Re: [PATCH] blk_iocost: fix more out of bound shifts

[Jens Axboe]

On Thu, 22 Aug 2024 08:41:36 -0700, Konstantin Ovsepian wrote:
> 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
> ...
> 
> [...]

Applied, thanks!

[1/1] blk_iocost: fix more out of bound shifts
      commit: 9bce8005ec0dcb23a58300e8522fe4a31da606fa

Best regards,
-- 
Jens Axboe