Solar Designer <solar@xxxxxxxxxxxx> writes:
> Hi Michal,
>
> On Mon, Feb 07, 2022 at 01:17:55PM +0100, Michal Koutný wrote:
>> The check is currently against the current->cred but since those are
>> going to change and we want to check RLIMIT_NPROC condition after the
>> switch, supply the capability check with the new cred.
>> But since we're checking new_user being INIT_USER any new cred's
>> capability-based allowance may be redundant when the check fails and the
>> alternative solution would be revert of the commit 2863643fb8b9
>> ("set_user: add capability check when rlimit(RLIMIT_NPROC) exceeds")
>>
>> Fixes: 2863643fb8b9 ("set_user: add capability check when rlimit(RLIMIT_NPROC) exceeds")
>>
>> Cc: Solar Designer <solar@xxxxxxxxxxxx>
>> Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
>> Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
>> ---
>> kernel/sys.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sys.c b/kernel/sys.c
>> index 8ea20912103a..48c90dcceff3 100644
>> --- a/kernel/sys.c
>> +++ b/kernel/sys.c
>> @@ -481,7 +481,8 @@ static int set_user(struct cred *new)
>> */
>> if (ucounts_limit_cmp(new->ucounts, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)) >= 0 &&
>> new_user != INIT_USER &&
>> - !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
>> + !security_capable(new, &init_user_ns, CAP_SYS_RESOURCE, CAP_OPT_NONE) &&
>> + !security_capable(new, &init_user_ns, CAP_SYS_ADMIN, CAP_OPT_NONE))
>> current->flags |= PF_NPROC_EXCEEDED;
>> else
>> current->flags &= ~PF_NPROC_EXCEEDED;
>
> Thank you for working on this and CC'ing me on it. This is related to
> the discussion Christian and I had in September:
>
> https://lore.kernel.org/all/20210913100140.bxqlg47pushoqa3r@wittgenstein/
>
> Christian was going to revert 2863643fb8b9, but apparently that never
> happened. Back then, I also suggested:
>
> "Alternatively, we could postpone the set_user() calls until we're
> running with the new user's capabilities, but that's an invasive change
> that's likely to create its own issues."
Back then you mentioned that apache suexec was broken. Do you have
any more details?
I would like to make certain the apache suexec issue is fixed but
without a few details I can't do that. I tried looking but I can't
find an public report about apache suexec being broken.
My goal is to come up with a very careful and conservative set of
patches that fix all of the known issues with RLIMIT_NPROC.
Eric
