4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Justin Stitt justinstitt@google.com
[ Upstream commit 87d571d6fb77ec342a985afa8744bb9bb75b3622 ]
Using syzkaller alongside the newly reintroduced signed integer overflow sanitizer spits out this report:
UBSAN: signed-integer-overflow in ../kernel/time/ntp.c:461:16 9223372036854775807 + 500 cannot be represented in type 'long' Call Trace: handle_overflow+0x171/0x1b0 second_overflow+0x2d6/0x500 accumulate_nsecs_to_secs+0x60/0x160 timekeeping_advance+0x1fe/0x890 update_wall_time+0x10/0x30
time_maxerror is unconditionally incremented and the result is checked against NTP_PHASE_LIMIT, but the increment itself can overflow, resulting in wrap-around to negative space.
Before commit eea83d896e31 ("ntp: NTP4 user space bits update") the user supplied value was sanity checked to be in the operating range. That change removed the sanity check and relied on clamping in handle_overflow() which does not work correctly when the user supplied value is in the overflow zone of the '+ 500' operation.
The operation requires CAP_SYS_TIME and the side effect of the overflow is NTP getting out of sync.
Miroslav confirmed that the input value should be clamped to the operating range and the same applies to time_esterror. The latter is not used by the kernel, but the value still should be in the operating range as it was before the sanity check got removed.
Clamp them to the operating range.
[ tglx: Changed it to clamping and included time_esterror ]
Fixes: eea83d896e31 ("ntp: NTP4 user space bits update") Signed-off-by: Justin Stitt justinstitt@google.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Miroslav Lichvar mlichvar@redhat.com Link: https://lore.kernel.org/all/20240517-b4-sio-ntp-usec-v2-1-d539180f2b79@googl... Closes: https://github.com/KSPP/linux/issues/354 Signed-off-by: Sasha Levin sashal@kernel.org [ cast things to __kernel_long_t to fix compiler warnings - gregkh ] Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/time/ntp.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -686,10 +686,10 @@ static inline void process_adjtimex_mode }
if (txc->modes & ADJ_MAXERROR) - time_maxerror = txc->maxerror; + time_maxerror = clamp(txc->maxerror, (__kernel_long_t)0, (__kernel_long_t)NTP_PHASE_LIMIT);
if (txc->modes & ADJ_ESTERROR) - time_esterror = txc->esterror; + time_esterror = clamp(txc->esterror, (__kernel_long_t)0, (__kernel_long_t)NTP_PHASE_LIMIT);
if (txc->modes & ADJ_TIMECONST) { time_constant = txc->constant;