Messages in this thread | | | Date | Fri, 11 Feb 2022 12:34:54 +0100 | From | Alexey Gladkov <> | Subject | Re: [PATCH 6/8] ucounts: Handle inc_rlimit_ucounts wrapping in fork |
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On Thu, Feb 10, 2022 at 08:13:22PM -0600, Eric W. Biederman wrote: > Move inc_rlimit_ucounts from copy_creds into copy_process immediately > after copy_creds where it can be called exactly once. Test for and > handle it when inc_rlimit_ucounts returns LONG_MAX indicating the > count has wrapped. > > This is good hygenine and fixes a theoretical bug. In practice > PID_MAX_LIMIT is at most 2^22 so there is not a chance the number of > processes would ever wrap even on an architecture with a 32bit long. > > Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts") > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> > --- > kernel/cred.c | 2 -- > kernel/fork.c | 2 ++ > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/cred.c b/kernel/cred.c > index 229cff081167..96d5fd6ff26f 100644 > --- a/kernel/cred.c > +++ b/kernel/cred.c > @@ -358,7 +358,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) > kdebug("share_creds(%p{%d,%d})", > p->cred, atomic_read(&p->cred->usage), > read_cred_subscribers(p->cred)); > - inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); > return 0; > } > > @@ -395,7 +394,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) > #endif > > p->cred = p->real_cred = get_cred(new); > - inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); > alter_cred_subscribers(new, 2); > validate_creds(new); > return 0; > diff --git a/kernel/fork.c b/kernel/fork.c > index 6f62d37f3650..69333078259c 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -2026,6 +2026,8 @@ static __latent_entropy struct task_struct *copy_process( > goto bad_fork_free; > > retval = -EAGAIN; > + if (inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1) == LONG_MAX) > + goto bad_fork_cleanup_count; > if (is_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) { > if ((task_ucounts(p) != &init_ucounts) && > !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
It might make sense to do something like:
if (inc_rlimit_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1, rlimit(RLIMIT_NPROC)) == LONG_MAX) { if ((task_ucounts(p) != &init_ucounts) && !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
and the new function:
long inc_rlimit_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, long v, unsigned long rlimit) { struct ucounts *iter; long ret = 0; long max = rlimit; if (rlimit > LONG_MAX) max = LONG_MAX; for (iter = ucounts; iter; iter = iter->ns->ucounts) { long new = atomic_long_add_return(v, &iter->ucount[type]); if (new < 0 || new > max) ret = LONG_MAX; else if (iter == ucounts) ret = new; max = READ_ONCE(iter->ns->ucount_max[type]); } return ret; }
This will avoid double checking the same userns tree.
Or even modify inc_rlimit_ucounts. This function is used elsewhere like this:
msgqueue = inc_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes); if (msgqueue == LONG_MAX || msgqueue > rlimit(RLIMIT_MSGQUEUE)) {
memlock = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); if (!allowed && (memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) {
In all cases, we have max value for comparison.
-- Rgrds, legion
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