Patch "blk-iocost: fix divide by 0 error in calc_lcoefs()" has been added to the 5.4-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 divide by 0 error in calc_lcoefs()

to the 5.4-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-divide-by-0-error-in-calc_lcoefs.patch
and it can be found in the queue-5.4 subdirectory.

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



commit 7b076b42af80e238a1476a626c628fe9181970bd
Author: Li Nan <linan122@xxxxxxxxxx>
Date:   Tue Jan 17 15:08:05 2023 +0800

    blk-iocost: fix divide by 0 error in calc_lcoefs()
    
    [ Upstream commit 984af1e66b4126cf145153661cc24c213e2ec231 ]
    
    echo max of u64 to cost.model can cause divide by 0 error.
    
      # echo 8:0 rbps=18446744073709551615 > /sys/fs/cgroup/io.cost.model
    
      divide error: 0000 [#1] PREEMPT SMP
      RIP: 0010:calc_lcoefs+0x4c/0xc0
      Call Trace:
       <TASK>
       ioc_refresh_params+0x2b3/0x4f0
       ioc_cost_model_write+0x3cb/0x4c0
       ? _copy_from_iter+0x6d/0x6c0
       ? kernfs_fop_write_iter+0xfc/0x270
       cgroup_file_write+0xa0/0x200
       kernfs_fop_write_iter+0x17d/0x270
       vfs_write+0x414/0x620
       ksys_write+0x73/0x160
       __x64_sys_write+0x1e/0x30
       do_syscall_64+0x35/0x80
       entry_SYSCALL_64_after_hwframe+0x63/0xcd
    
    calc_lcoefs() uses the input value of cost.model in DIV_ROUND_UP_ULL,
    overflow would happen if bps plus IOC_PAGE_SIZE is greater than
    ULLONG_MAX, it can cause divide by 0 error.
    
    Fix the problem by setting basecost
    
    Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
    Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
    Acked-by: Tejun Heo <tj@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230117070806.3857142-5-yukuai1@xxxxxxxxxxxxxxx
    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 ef287c33d6d97..4fdc8858a69a9 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -785,9 +785,14 @@ static void calc_lcoefs(u64 bps, u64 seqiops, u64 randiops,
 
 	*page = *seqio = *randio = 0;
 
-	if (bps)
-		*page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
-					   DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
+	if (bps) {
+		u64 bps_pages = DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE);
+
+		if (bps_pages)
+			*page = DIV64_U64_ROUND_UP(VTIME_PER_SEC, bps_pages);
+		else
+			*page = 1;
+	}
 
 	if (seqiops) {
 		v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, seqiops);