CVE-2026-90100 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
ptp: netc: fix period truncation and potential divide-by-zero in PEROUT
The max_period bound in net_timer_enable_perout() was computed as:
max_period = (u64)NETC_TMR_DEFAULT_FIPER + integral_period;
which exceeds U32_MAX when integral_period > 0 (e.g. 0x100000002 for the default 333333333 Hz clock). A period_ns that passes this check but exceeds U32_MAX is then silently truncated when stored into the u32 struct netc_pp::period field.
A truncated value of zero can reach netc_timer_set_perout_alarm(), where the local u32 period variable would also be 0, causing a divide-by-zero in roundup_u64(delta, period) whenever the stime < min_time branch is taken (which always happens for a start time of {0, 0}).
Additionally, netc_timer_enable_periodic_pulse() and netc_timer_enable_fiper() both compute:
fiper = pp->period - integral_period;
A zero pp->period results in an unsigned wraparound to 0xFFFFFFFD, mis-programming the FIPER hardware register.
Fix all three issues by capping max_period at NETC_TMR_DEFAULT_FIPER (0xFFFFFFFF). This ensures that any period_ns passing the range check fits in a u32 without truncation, so the stored value is always valid and non-zero. The accepted range is reduced by integral_period ns (typically only a few nanoseconds), which is negligible in practice.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel driver for the Netronome Network Controller contains a critical integer overflow vulnerability within its Precision Time Protocol implementation, specifically affecting the periodic output configuration logic. This flaw originates from an incorrect calculation of the maximum allowable period value during the initialization of hardware timers. The function netc_timer_enable_perout computes this upper bound by adding a default frequency interval to an integral period offset. Because both operands are treated as unsigned 64-bit integers, their sum can easily exceed the maximum limit of a standard 32-bit unsigned integer when the integral period is non-zero. This miscalculation allows values that are technically out of range for the underlying hardware register storage to pass initial validation checks, setting the stage for subsequent data corruption and system instability.
The primary technical consequence of this overflow is silent truncation of the period value upon assignment to a 32-bit structure field. When a user-space application requests a periodic output with a duration that exceeds U32_MAX but passes the flawed upper-bound check, the high-order bits are discarded during storage. This results in a significantly smaller or potentially zeroed-out period value being written into the kernel data structures. Such truncation fundamentally alters the intended timing behavior of the hardware timer, leading to unpredictable pulse generation and synchronization errors that can disrupt time-sensitive network operations dependent on accurate Precision Time Protocol signaling.
A more severe operational impact arises when this truncated value resolves to exactly zero before reaching the alarm configuration routine. Inside netc_timer_set_perout_alarm, a local variable holds this period value which is subsequently used as a divisor in a roundup operation. If the start time condition triggers a specific code path involving division by this period variable, the system encounters a divide-by-zero exception. In kernel space, such an arithmetic error typically results in an immediate kernel panic or denial of service, effectively crashing the host machine and halting all network processing capabilities until a reboot occurs. This represents a significant availability risk for systems relying on continuous uptime and precise timekeeping services.
Furthermore, the vulnerability extends to other timer configuration functions that perform subtraction operations involving the corrupted period field. Functions such as netc_timer_enable_periodic_pulse and netc_timer_enable_fiper calculate hardware register values by subtracting an integral offset from the stored period. If the stored period has been truncated to zero due to the initial overflow, this subtraction results in a large unsigned integer wraparound value rather than a negative number or error code. This erroneous result is then programmed directly into FIPER hardware registers, misconfiguring the clock source and potentially causing further timing anomalies or hardware malfunctions that are difficult to diagnose without deep kernel-level inspection.
The resolution involves capping the maximum allowed period at the default frequency interval value, which corresponds to the maximum representable 32-bit unsigned integer. By enforcing this strict upper bound during validation, the driver ensures that any accepted period value fits safely within a u32 variable without truncation. This fix guarantees that the stored period remains non-zero and valid for subsequent arithmetic operations, thereby eliminating both the divide-by-zero condition and the register misconfiguration risks. The adjustment reduces the acceptable range by only a negligible amount of nanoseconds in typical configurations, preserving functional utility while restoring critical security and stability properties to the network controller driver.
This vulnerability aligns with CWE-190 Integer Overflow or Wraparound due to improper handling of large integer values during arithmetic operations. It also relates to CWE-362 Concurrent Execution Using Shared Resource with Improper Synchronization if the race condition allows multiple threads to trigger the overflow before validation, though the primary issue is computational logic rather than concurrency per se. From an ATT&CK perspective, this flaw could be exploited for Denial of Service (T1499) by triggering a kernel panic through crafted ioctl calls or configuration requests targeting the PTP subsystem. Mitigation strategies include applying the provided kernel patch to cap period values appropriately and ensuring that input validation routines strictly enforce 32-bit boundaries before any hardware register programming occurs.