UBUNTU-CVE-2026-72121: High severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: can: bcm: add locking when updating filter and timer values KCSAN detected a simultaneous access to timer values that can be overwritten in bcmrxsetup() when updating timer and filter content while bcmrxhandler(), bcmrxtimeouthandler() or bcmrxthrhandler() run concurrently on incoming CAN traffic. Protect the timer (ival1/ival2/ktival1/ktival2/ktlastmsg) and filter (nframes/flags/frames/lastframes) updates in bcmrxsetup() with a new per-op bcmrxupdatelock, taken with the matching scope in the RX handlers. memcpyfrommsg() is staged into a temporary buffer before the lock is taken, since it can sleep and must not run under a spinlock. hrtimercancel() is always called without bcmrxupdatelock held, since bcmrxtimeouthandler()/bcmrxthrhandler() take the same lock and a running callback would otherwise deadlock against the canceller. Also close a related race: bcmrxsetup() cleared the RTR flag in the stored reply frame's canid as a separate, unprotected step after the frame content was already installed, so a concurrent bcmrxhandler() could transmit a stale reply with CANRTRFLAG still set. Fold that normalization into the initial frame preparation instead (on the staged buffer for updates, directly on op->frames pre-registration for new ops), so the installed frame is always atomically self-consistent. bcmrxhandler()'s RXRTRFRAME check now takes a lock-protected snapshot of op->flags before deciding whether to call bcmcantx(), but does not hold the lock across that call. Also take a lock-protected snapshot of the currframe in bcmcantx() to avoid partly overwrites by content updates in bcmtxsetup(). Finally check if a TXRESETMULTIIDX/SETTIMER might have reset op->currframe between the two locked sections in bcmcantx(). Omit calling hrtimerforward() with zero interval in bcmrxthrhandler(). ktival2 may have been concurrently cleared by bcmrxsetup() before it cancels this timer, so check ktival2 inside the bcmrxupdatelock.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1117.124~20.04.1 - Upgrade
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ubuntu/linux-azure-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1123.132~20.04.1 - Upgrade
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ubuntu/linux-azure-fde-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1122.131~20.04.1 - Upgrade
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ubuntu/linux-gcp-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1118.128~20.04.1 - Upgrade
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ubuntu/linux-hwe-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-198.208~20.04.1 - Upgrade
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ubuntu/linux-ibm-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1111.115~20.04.1 - Upgrade
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ubuntu/linux-intel-iotg-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1112.118~20.04.1 - Upgrade
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ubuntu/linux-lowlatency-hwe-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-195.205~20.04.1 - Upgrade
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ubuntu/linux-oracle-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1114.120~20.04.1 - Upgrade
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ubuntu/linux-riscv-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1111.115~20.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 5.15.0-198.208 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 5.15.0-1117.124 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 5.15.0-1123.132 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 6.8.0-1067.70 - Upgrade
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ubuntu/linux-aws-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1067.70+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-147.147+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-38.38 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Compensating control
In bcm_rx_setup(), protect updates to timer fields ival1, ival2, kt_ival1, kt_ival2, kt_lastmsg and filter fields nframes, flags, frames, last_frames with a per-operation bcm_rx_update_lock; acquire the same lock in bcm_rx_handler(), bcm_rx_timeout_handler(), and bcm_rx_thr_handler() for matching access.
- Compensating control
In bcm_rx_handler(), take a lock-protected snapshot of op->flags before evaluating RX_RTR_FRAME and deciding whether to call bcm_can_tx(), but do not hold bcm_rx_update_lock across the bcm_can_tx() call.
- Compensating control
In bcm_can_tx(), take a lock-protected snapshot of currframe and check whether TX_RESET_MULTI_IDX or SETTIMER reset op->currframe between the two locked sections.
- Compensating control
Normalize the RTR flag while preparing the initial frame: clear CAN_RTR_FLAG on the staged buffer before updates are installed and directly on op->frames before registering new operations, so the installed frame is atomically self-consistent.
- Compensating control
Stage memcpy_from_msg() into a temporary buffer before acquiring the spinlock, because memcpy_from_msg() can sleep.
- Compensating control
Do not call hrtimer_forward() with a zero interval in bcm_rx_thr_handler().
- Compensating control
Call hrtimer_cancel() without holding bcm_rx_update_lock; before cancelling the timer, check kt_ival2 while holding bcm_rx_update_lock because bcm_rx_setup() may have cleared it concurrently.