The following commit has been merged into the timers/urgent branch of tip:
Commit-ID: 06c03c8edce333b9ad9c6b207d93d3a5ae7c10c0
Gitweb: https://git.kernel.org/tip/06c03c8edce333b9ad9c6b207d93d3a5ae7c10c0
Author: Justin Stitt <justinstitt@xxxxxxxxxx>
AuthorDate: Fri, 17 May 2024 00:47:10
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Mon, 05 Aug 2024 16:14:14 +02:00
ntp: Safeguard against time_constant overflow
Using syzkaller with the recently reintroduced signed integer overflow
sanitizer produces this UBSAN report:
UBSAN: signed-integer-overflow in ../kernel/time/ntp.c:738:18
9223372036854775806 + 4 cannot be represented in type 'long'
Call Trace:
handle_overflow+0x171/0x1b0
__do_adjtimex+0x1236/0x1440
do_adjtimex+0x2be/0x740
The user supplied time_constant value is incremented by four and then
clamped to the operating range.
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 after incrementing which
does not work correctly when the user supplied value is in the overflow
zone of the '+ 4' operation.
The operation requires CAP_SYS_TIME and the side effect of the overflow is
NTP getting out of sync.
Similar to the fixups for time_maxerror and time_esterror, clamp the user
space supplied value to the operating range.
[ tglx: Switch to clamping ]
Fixes: eea83d896e31 ("ntp: NTP4 user space bits update")
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/20240517-b4-sio-ntp-c-v2-1-f3a80096f36f@xxxxxxxxxx
Closes: https://github.com/KSPP/linux/issues/352
---
kernel/time/ntp.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 502e1e5..8d2dd21 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -733,11 +733,10 @@ static inline void process_adjtimex_modes(const struct __kernel_timex *txc,
time_esterror = clamp(txc->esterror, 0, NTP_PHASE_LIMIT);
if (txc->modes & ADJ_TIMECONST) {
- time_constant = txc->constant;
+ time_constant = clamp(txc->constant, 0, MAXTC);
if (!(time_status & STA_NANO))
time_constant += 4;
- time_constant = min(time_constant, (long)MAXTC);
- time_constant = max(time_constant, 0l);
+ time_constant = clamp(time_constant, 0, MAXTC);
}
if (txc->modes & ADJ_TAI &&
|