Messages in this thread Patch in this message | | | From | "Eric W. Biederman" <> | Date | Mon, 14 Mar 2022 10:21:10 -0500 | Subject | Re: [PATCH v2] mm/mlock: fix potential imbalanced rlimit ucounts adjustment |
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Miaohe Lin <linmiaohe@huawei.com> writes:
> user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So > the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix > this by resetting allowed to 0.
This fix looks correct. But the ability for people to follow and read the code seems questionable. I saw in v1 of this patch Hugh originally misread the logic.
Could we instead change the code to leave lock_limit at ULONG_MAX aka RLIM_INFINITY, leave initialized to 0, and not even need a special case of RLIM_INFINITY as nothing can be greater that ULONG_MAX?
Something like this?
diff --git a/mm/mlock.c b/mm/mlock.c index 8f584eddd305..e7eabf5193ab 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -827,13 +827,12 @@ int user_shm_lock(size_t size, struct ucounts *ucounts) locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; lock_limit = rlimit(RLIMIT_MEMLOCK); - if (lock_limit == RLIM_INFINITY) - allowed = 1; - lock_limit >>= PAGE_SHIFT; + if (lock_limit != RLIM_INFINITY) + lock_limit >>= PAGE_SHIFT; spin_lock(&shmlock_user_lock); memlock = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); - if (!allowed && (memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) { + if ((memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) { dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); goto out; } > > Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts") > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > Acked-by: Hugh Dickins <hughd@google.com> > --- > v1->v2: > correct Fixes tag and collect Acked-by tag > Thanks Hugh for review! > --- > mm/mlock.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/mlock.c b/mm/mlock.c > index 29372c0eebe5..efd2dd2943de 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts) > } > if (!get_ucounts(ucounts)) { > dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); > + allowed = 0; > goto out; > } > allowed = 1;
Eric
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