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Mon, 03 Aug 2026 02:14:40 -0700 (PDT) From: Sureshkumar S To: Marc Kleine-Budde , Vincent Mailhol Cc: Oliver Hartkopp , linux-can@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Sureshkumar S Subject: [PATCH net 0/2] can: bittiming: fix two defects in the userspace bitrate conversion Date: Mon, 3 Aug 2026 09:14:24 +0000 Message-ID: <20260803091426.29050-1-ssureshmsd7@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit can_calc_bittiming() converts a userspace supplied bitrate into hardware timing parameters. Two defects in that conversion are fixed here, both reachable through IFLA_CAN_BITTIMING on any CAN device that provides a bittiming_const, and both caused by 32 bit arithmetic on a value that userspace fully controls. Patch 1 fixes a divide-by-zero. The 32 bit tsegall * bt->bitrate product wraps to zero for bitrates carrying enough factors of two, and the following division faults. A bitrate of 16777216 is already enough, which is below the 20 Mbit/s CAN XL data bitrate ceiling. Patch 2 fixes the candidate rating, which applies abs() to an unsigned subtraction. A wrapped difference is read back as a small error, so a bitrate far outside what the controller can reach passes the 5% gate and is silently accepted instead of rejected. Both were found with a netlink fuzzer against dummy_can and verified under KASAN in QEMU. Testing covered the unpatched tree, patch 1 alone and the full series: bitrates from 125 kbit/s to 10 Mbit/s produce byte-identical bittiming at every step, patch 1 alone removes the oops, and patch 2 turns the silently accepted out-of-range bitrates into -EINVAL. Sureshkumar S (2): can: bittiming: fix divide-by-zero in can_calc_bittiming() can: bittiming: fix bitrate error calculation on unsigned operands drivers/net/can/dev/calc_bittiming.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) base-commit: af39eb111ce6b5eba9c08513b62c4868eb7e7fd5 -- 2.43.0