Re: [PATCH -next 1/2] blk-iocost: fix divide by 0 error in calc_lcoefs()
From: Andreas Herrmann <hidden>
Date: 2022-11-25 09:55:48
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On Thu, Nov 24, 2022 at 10:06:34PM +0800, Li Nan wrote:
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.I_LCOEF_MAX is introduced to prevent it. Signed-off-by: Li Nan <redacted> --- block/blk-iocost.c | 5 +++++ 1 file changed, 5 insertions(+)
Looks good. Reviewed-by: Andreas Herrmann <redacted>
quoted hunk ↗ jump to hunk
diff --git a/block/blk-iocost.c b/block/blk-iocost.c index f01359906c83..a38a5324bf10 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c@@ -306,6 +306,9 @@ enum { IOC_PAGE_SIZE = 1 << IOC_PAGE_SHIFT, IOC_SECT_TO_PAGE_SHIFT = IOC_PAGE_SHIFT - SECTOR_SHIFT, + /* avoid overflow */ + I_LCOEF_MAX = ULLONG_MAX - IOC_PAGE_SIZE, + /* if apart further than 16M, consider randio for linear model */ LCOEF_RANDIO_PAGES = 4096, };@@ -3406,6 +3409,8 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input, goto einval; if (match_u64(&args[0], &v)) goto einval; + if (v > I_LCOEF_MAX) + goto einval; u[tok] = v; user = true; }-- 2.31.1
-- Regards, Andreas SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nürnberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Martje Boudien Moerman (HRB 36809, AG Nürnberg)