CVE-2025-21922 — ppp: Fix KMSAN uninit-value warning with bpf

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

ppp: Fix KMSAN uninit-value warning with bpf

Syzbot caught an "KMSAN: uninit-value" warning [1], which is caused by the ppp driver not initializing a 2-byte header when using socket filter.

The following code can generate a PPP filter BPF program: ''' struct bpf_program fp; pcap_t *handle; handle = pcap_open_dead(DLT_PPP_PPPD, 65535); pcap_compile(handle, &fp, "ip and outbound", 0, 0); bpf_dump(&fp, 1); ''' Its output is: ''' (000) ldh [2] (001) jeq #0x21 jt 2 jf 5 (002) ldb [0] (003) jeq #0x1 jt 4 jf 5 (004) ret #65535 (005) ret #0 ''' Wen can find similar code at the following link: https://github.com/ppp-project/ppp/blob/master/pppd/options.c#L1680 The maintainer of this code repository is also the original maintainer of the ppp driver.

As you can see the BPF program skips 2 bytes of data and then reads the 'Protocol' field to determine if it's an IP packet. Then it read the first byte of the first 2 bytes to determine the direction.

The issue is that only the first byte indicating direction is initialized in current ppp driver code while the second byte is not initialized.

For normal BPF programs generated by libpcap, uninitialized data won't be used, so it's not a problem. However, for carefully crafted BPF programs, such as those generated by syzkaller [2], which start reading from offset 0, the uninitialized data will be used and caught by KMSAN.

[1] https://syzkaller.appspot.com/bug?extid=8532…

USN-7510-1 — linux, linux-gkeop, linux-ibm, linux-ibm-5.15, linux-intel-iotg, linux-kvm, linux-lowlatency, linux-lowlatency-hwe-5.15…

Affected: Ubuntu:20.04:LTS: linux-ibm-5.15, Ubuntu:20.04:LTS: linux-lowlatency-hwe-5.15, Ubuntu:20.04:LTS: linux-oracle-5.15, Ubuntu:22.04:LTS: linux, Ubuntu:22.04:LTS: linux-gkeop, Ubuntu:22.04:LTS: linux-ibm, Ubuntu:22.04:LTS: linux-intel-iotg, Ubuntu:22.04:LTS: linux-kvm, Ubuntu:22.04:LTS: linux-lowlatency, Ubuntu:22.04:LTS: linux-nvidia and 1 more

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - ARM64 architecture; - PowerPC architecture; - x86 architecture; - Block layer subsystem; - Network block device driver; - Bus devices; - Character device driver; - TPM device driver; - Clock framework and drivers; - GPIO subsystem; - GPU drivers; - HID subsystem; - I2C subsystem; - InfiniBand drivers; - Media drivers; - NVIDIA Tegra memory controller driver; - Network drivers; - PCI subsystem; - PPS (Pulse Per Second) driver; - PTP clock framework; - RapidIO drivers; - Real Time Clock drivers; - SLIMbus drivers; - QCOM SoC drivers; - Trusted Execution Environment drivers; - TTY drivers; - USB DSL drivers; - USB Device Class drivers; - USB core drivers; - USB Gadget drivers; - USB Host Controller drivers; - Renesas USBHS Controller drivers; - ACRN Hypervisor Service Module driver; - File systems infrastructure; - BTRFS file system; - F2FS file system; - Network file system (NFS) server daemon; - NILFS2 file system; - Overlay file system; - SMB network file system; - UBI file system; - KVM subsystem; - L3 Master device support module; - Process Accounting mechanism; - Padata parallel execution mechanism; - printk logging mechanism; - Scheduler infrastructure; - Timer subsystem; - Tracing infrastructure…

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CVE-2025-21922 — ppp: Fix KMSAN uninit-value warning with bpf

USN-7510-1 — linux, linux-gkeop, linux-ibm, linux-ibm-5.15, linux-intel-iotg, linux-kvm, linux-lowlatency, linux-lowlatency-hwe-5.15…