2021-09-23 02:11:34

by Chen Jun

Subject: [PATCH v3 1/1] mm: Fix the uninitialized use in overcommit_policy_handler

An unexpected value of /proc/sys/vm/overcommit_memory we will get,
after running the following program.

int main()
{
int fd = open("/proc/sys/vm/overcommit_memory", O_RDWR)
write(fd, "1", 1);
write(fd, "2", 1);
close(fd);
}

write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
proc_dointvec_minmax will return 0 without setting new_policy.

t.data = &new_policy;
ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
-->do_proc_dointvec
-->__do_proc_dointvec
if (write) {
if (proc_first_pos_non_zero_ignore(ppos, table))
goto out;

sysctl_overcommit_memory = new_policy;

so sysctl_overcommit_memory will be set to an uninitialized value.

Check whether new_policy has been changed by proc_dointvec_minmax.

Fixes: 56f3547bfa4d ("mm: adjust vm_committed_as_batch according to vm overcommit policy"
Signed-off-by: Chen Jun <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Reviewed-by: Feng Tang <[email protected]>

---

v3:
* Correct commit message.

v2:
* Check whether new_policy has been changed by proc_dointvec_minmax.

mm/util.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 4ddb6e186dd5..d5be67771850 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -756,7 +756,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
size_t *lenp, loff_t *ppos)
{
struct ctl_table t;
- int new_policy;
+ int new_policy = -1;
int ret;

/*
@@ -774,7 +774,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
t = *table;
t.data = &new_policy;
ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
- if (ret)
+ if (ret || new_policy == -1)
return ret;

mm_compute_batch(new_policy);
--
2.17.1

2021-09-24 02:24:13

by Andrew Morton

Subject: Re: [PATCH v3 1/1] mm: Fix the uninitialized use in overcommit_policy_handler

On Thu, 23 Sep 2021 02:05:24 +0000 Chen Jun <[email protected]> wrote:

> An unexpected value of /proc/sys/vm/overcommit_memory we will get,
> after running the following program.
>
> int main()
> {
> int fd = open("/proc/sys/vm/overcommit_memory", O_RDWR)
> write(fd, "1", 1);
> write(fd, "2", 1);
> close(fd);
> }
>
> write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
> proc_dointvec_minmax will return 0 without setting new_policy.
>
> t.data = &new_policy;
> ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
> -->do_proc_dointvec
> -->__do_proc_dointvec
> if (write) {
> if (proc_first_pos_non_zero_ignore(ppos, table))
> goto out;
>
> sysctl_overcommit_memory = new_policy;
>
> so sysctl_overcommit_memory will be set to an uninitialized value.
>
> Check whether new_policy has been changed by proc_dointvec_minmax.
>

Thanks. I added a cc:stable to this, so the fix will be backported
into earlier kernels.

2021-09-24 02:43:58

by Kefeng Wang

Subject: Re: [PATCH v3 1/1] mm: Fix the uninitialized use in overcommit_policy_handler

On 2021/9/24 10:23, Andrew Morton wrote:
> On Thu, 23 Sep 2021 02:05:24 +0000 Chen Jun <[email protected]> wrote:
>
>> An unexpected value of /proc/sys/vm/overcommit_memory we will get,
>> after running the following program.
>>
>> int main()
>> {
>> int fd = open("/proc/sys/vm/overcommit_memory", O_RDWR)

Hi Andrew，

missing  ';' here,

> Thanks. I added a cc:stable to this, so the fix will be backported
> into earlier kernels.

...  and the Fixes tag miss a ')' in the end ,  please help to add them :)

Reviewed-by: Kefeng Wang <[email protected]>