On Sat, Nov 02, 2024 at 12:28:38AM +0100, Alexey Gladkov wrote: > On Thu, Oct 31, 2024 at 08:04:38PM +0000, Roman Gushchin wrote: > > Prior to commit d64696905554 ("Reimplement RLIMIT_SIGPENDING on top of > > ucounts") UCOUNT_RLIMIT_SIGPENDING rlimit was not enforced for a class > > of signals. However now it's enforced unconditionally, even if > > override_rlimit is set. This behavior change caused production issues. > > > > For example, if the limit is reached and a process receives a SIGSEGV > > signal, sigqueue_alloc fails to allocate the necessary resources for the > > signal delivery, preventing the signal from being delivered with > > siginfo. This prevents the process from correctly identifying the fault > > address and handling the error. From the user-space perspective, > > applications are unaware that the limit has been reached and that the > > siginfo is effectively 'corrupted'. This can lead to unpredictable > > behavior and crashes, as we observed with java applications. > > > > Fix this by passing override_rlimit into inc_rlimit_get_ucounts() and > > skip the comparison to max there if override_rlimit is set. This > > effectively restores the old behavior. > > > > Fixes: d64696905554 ("Reimplement RLIMIT_SIGPENDING on top of ucounts") > > Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx> > > Co-developed-by: Andrei Vagin <avagin@xxxxxxxxxx> > > Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx> > > Cc: Kees Cook <kees@xxxxxxxxxx> > > Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > > Cc: Alexey Gladkov <legion@xxxxxxxxxx> > > Cc: <stable@xxxxxxxxxxxxxxx> > > --- > > include/linux/user_namespace.h | 3 ++- > > kernel/signal.c | 3 ++- > > kernel/ucount.c | 5 +++-- > > 3 files changed, 7 insertions(+), 4 deletions(-) > > > > diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h > > index 3625096d5f85..7183e5aca282 100644 > > --- a/include/linux/user_namespace.h > > +++ b/include/linux/user_namespace.h > > @@ -141,7 +141,8 @@ static inline long get_rlimit_value(struct ucounts *ucounts, enum rlimit_type ty > > > > long inc_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v); > > bool dec_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v); > > -long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type); > > +long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type, > > + bool override_rlimit); > > void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum rlimit_type type); > > bool is_rlimit_overlimit(struct ucounts *ucounts, enum rlimit_type type, unsigned long max); > > > > diff --git a/kernel/signal.c b/kernel/signal.c > > index 4344860ffcac..cbabb2d05e0a 100644 > > --- a/kernel/signal.c > > +++ b/kernel/signal.c > > @@ -419,7 +419,8 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags, > > */ > > rcu_read_lock(); > > ucounts = task_ucounts(t); > > - sigpending = inc_rlimit_get_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING); > > + sigpending = inc_rlimit_get_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, > > + override_rlimit); > > rcu_read_unlock(); > > if (!sigpending) > > return NULL; > > diff --git a/kernel/ucount.c b/kernel/ucount.c > > index 16c0ea1cb432..046b3d57ebb4 100644 > > --- a/kernel/ucount.c > > +++ b/kernel/ucount.c > > @@ -307,7 +307,8 @@ void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum rlimit_type type) > > do_dec_rlimit_put_ucounts(ucounts, NULL, type); > > } > > > > -long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type) > > +long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type, > > + bool override_rlimit) > > { > > /* Caller must hold a reference to ucounts */ > > struct ucounts *iter; > > @@ -316,7 +317,7 @@ long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type) > > > > for (iter = ucounts; iter; iter = iter->ns->ucounts) { > > long new = atomic_long_add_return(1, &iter->rlimit[type]); > > - if (new < 0 || new > max) > > + if (new < 0 || (!override_rlimit && (new > max))) > > goto unwind; > > if (iter == ucounts) > > ret = new; > > It's a bad patch. If we do as you suggest, it will > do_dec_rlimit_put_ucounts() in case of overflow. This means you'll > break the counter and there will be an extra decrement in __sigqueue_free(). > We can't just ignore the overflow here. Hm, I don't think my code is changing anything in terms of the overflow handling. The (new < 0) handling is exactly the same as it was, the only difference is that (new > max) is allowed if override_rlimit is set. But new physically can't be larger than LONG_MAX, so there is no actual change if the limit is LONG_MAX. Maybe I'm missing something here, please, clarify. Thanks!