Patch "blk_iocost: fix more out of bound shifts" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    blk_iocost: fix more out of bound shifts

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     blk_iocost-fix-more-out-of-bound-shifts.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 4d9e154d7f7f28ff4afe694cfdeca9312bc6b844
Author: Konstantin Ovsepian <ovs@xxxxxx>
Date:   Thu Aug 22 08:41:36 2024 -0700

    blk_iocost: fix more out of bound shifts
    
    [ 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@xxxxxxxxxx>
    Signed-off-by: Konstantin Ovsepian <ovs@xxxxxx>
    Acked-by: Tejun Heo <tj@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240822154137.2627818-1-ovs@xxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index bfdb7b0cf49de..9654d1c2c20f8 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2068,7 +2068,7 @@ 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) {
@@ -2130,10 +2130,12 @@ 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);