On 2023/5/27 2:54, SeongJae Park wrote:
Hi Kefeng and syzbot,
On Fri, 26 May 2023 20:59:12 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
On 2023/5/26 19:51, syzbot wrote:
Hello,
syzbot found the following issue on:
HEAD commit: 44c026a73be8 Linux 6.4-rc3
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13a92b31280000
kernel config: https://syzkaller.appspot.com/x/.config?x=f389ffdf4e9ba3f0
dashboard link: https://syzkaller.appspot.com/bug?extid=841a46899768ec7bec67
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: i386
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/35f16ee05df7/disk-44c026a7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/10399498a570/vmlinux-44c026a7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5c72201ea4ba/bzImage-44c026a7.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+841a46899768ec7bec67@xxxxxxxxxxxxxxxxxxxxxxxxx
divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 13527 Comm: syz-executor.1 Not tainted 6.4.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/28/2023
RIP: 0010:damon_nr_accesses_to_accesses_bp mm/damon/core.c:491 [inline]
RIP: 0010:damon_nr_accesses_for_new_attrs mm/damon/core.c:497 [inline]
RIP: 0010:damon_update_monitoring_result mm/damon/core.c:506 [inline]
RIP: 0010:damon_update_monitoring_results mm/damon/core.c:534 [inline]
RIP: 0010:damon_set_attrs+0x224/0x460 mm/damon/core.c:555
Thank you for finding and reporting this bug!
The code of the problem is as below:
/* convert nr_accesses to access ratio in bp (per 10,000) */
static unsigned int damon_nr_accesses_to_accesses_bp(
unsigned int nr_accesses, struct damon_attrs *attrs)
{
unsigned int max_nr_accesses =
attrs->aggr_interval / attrs->sample_interval;
return nr_accesses * 10000 / max_nr_accesses;
}
The problem can happen when 'aggr_interval' is smaller than 'sample_interval',
because 'max_nr_accesses' becomes zero in the case, and resulting in divide by
zero.
Same problem is in damon_accesses_bp_to_nr_accesses().
make aggr_interval great than or equal sample_interval?
diff --git a/mm/damon/core.c b/mm/damon/core.c
index d9ef62047bf5..6fe1960f3d6b 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -525,8 +525,8 @@ static void damon_update_monitoring_results(struct
damon_ctx *ctx,
/* if any interval is zero, simply forgive conversion */
if (!old_attrs->sample_interval || !old_attrs->aggr_interval ||
- !new_attrs->sample_interval ||
- !new_attrs->aggr_interval)
+ !new_attrs->sample_interval || !new_attrs->aggr_interval ||
+ new_attrs->aggr_interval < new_attrs->sample_interval)
return;
Nice and effective fix! Nevertheless, I think aggregation interval smaller
than sample interval is just a wrong input. How about adding the check in
damon_set_attrs()'s already existing attributes validation, like below?
Yes, move the check into damon_set_attrs() is better, and it seems that
we could move all the check into it, and drop the old_attrs check in
damon_update_monitoring_results(), what's you option?
diff --git a/mm/damon/core.c b/mm/damon/core.c
index d9ef62047bf5..1647f7f1f708 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -523,12 +523,6 @@ static void damon_update_monitoring_results(struct
damon_ctx *ctx,
struct damon_target *t;
struct damon_region *r;
- /* if any interval is zero, simply forgive conversion */
- if (!old_attrs->sample_interval || !old_attrs->aggr_interval ||
- !new_attrs->sample_interval ||
- !new_attrs->aggr_interval)
- return;
-
damon_for_each_target(t, ctx)
damon_for_each_region(r, t)
damon_update_monitoring_result(
@@ -551,6 +545,10 @@ int damon_set_attrs(struct damon_ctx *ctx, struct
damon_attrs *attrs)
return -EINVAL;
if (attrs->min_nr_regions > attrs->max_nr_regions)
return -EINVAL;
+ if (attrs->sample_interval > attrs->aggr_interval)
+ return -EINVAL;
+ if (!attrs->sample_interval || !attrs->aggr_interval)
+ return -EINVAL;
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -580,6 +580,8 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
return -EINVAL;
if (attrs->min_nr_regions > attrs->max_nr_regions)
return -EINVAL;
+ if (attrs->aggr_interval < attrs->sample_interval)
+ return -EINVAL;
damon_update_monitoring_results(ctx, attrs);
ctx->attrs = *attrs;
Thanks,
SJ
