2022-02-16 16:10:43

by Eric W. Biederman

Subject: [PATCH v2 5/5] ucounts: Handle wrapping in is_ucounts_overlimit

While examining is_ucounts_overlimit and reading the various messages
I realized that is_ucounts_overlimit fails to deal with counts that
may have wrapped.

Being wrapped should be a transitory state for counts and they should
never be wrapped for long, but it can happen so handle it.

Cc: [email protected]
Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
Signed-off-by: "Eric W. Biederman" <[email protected]>
---
kernel/ucount.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index 65b597431c86..06ea04d44685 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -350,7 +350,8 @@ bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsign
if (rlimit > LONG_MAX)
max = LONG_MAX;
for (iter = ucounts; iter; iter = iter->ns->ucounts) {
- if (get_ucounts_value(iter, type) > max)
+ long val = get_ucounts_value(iter, type);
+ if (val < 0 || val > max)
return true;
max = READ_ONCE(iter->ns->ucount_max[type]);
}
--
2.29.2

2022-02-17 01:29:17

by Shuah Khan

Subject: Re: [PATCH v2 5/5] ucounts: Handle wrapping in is_ucounts_overlimit

On 2/16/22 8:58 AM, Eric W. Biederman wrote:
> While examining is_ucounts_overlimit and reading the various messages
> I realized that is_ucounts_overlimit fails to deal with counts that
> may have wrapped.
>
> Being wrapped should be a transitory state for counts and they should
> never be wrapped for long, but it can happen so handle it.
>
> Cc: [email protected]
> Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
> Signed-off-by: "Eric W. Biederman" <[email protected]>
> ---
> kernel/ucount.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 65b597431c86..06ea04d44685 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -350,7 +350,8 @@ bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsign
> if (rlimit > LONG_MAX)
> max = LONG_MAX;
> for (iter = ucounts; iter; iter = iter->ns->ucounts) {
> - if (get_ucounts_value(iter, type) > max)
> + long val = get_ucounts_value(iter, type);
> + if (val < 0 || val > max)
> return true;
> max = READ_ONCE(iter->ns->ucount_max[type]);
> }
>

This addresses the concerns about overflow.

Reviewed-by: Shuah Khan <[email protected]>

thanks,
-- Shuah