In the Linux kernel, the following vulnerability has been resolved:
cifs: fix DFS traversal oops without CONFIG_CIFS_DFS_UPCALL
When compiled with CONFIG_CIFS_DFS_UPCALL disabled, cifs_dfs_d_automount is NULL. cifs.ko logic for mapping CIFS_FATTR_DFS_REFERRAL attributes to S_AUTOMOUNT and corresponding dentry flags is retained regardless of CONFIG_CIFS_DFS_UPCALL, leading to a NULL pointer dereference in VFS follow_automount() when traversing a DFS referral link: BUG: kernel NULL pointer dereference, address: 0000000000000000 ... Call Trace: <TASK> __traverse_mounts+0xb5/0x220 ? cifs_revalidate_mapping+0x65/0xc0 [cifs] step_into+0x195/0x610 ? lookup_fast+0xe2/0xf0 path_lookupat+0x64/0x140 filename_lookup+0xc2/0x140 ? __create_object+0x299/0x380 ? kmem_cache_alloc+0x119/0x220 ? user_path_at_empty+0x31/0x50 user_path_at_empty+0x31/0x50 __x64_sys_chdir+0x2a/0xd0 ? exit_to_user_mode_prepare+0xca/0x100 do_syscall_64+0x42/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc
This fix adds an inline cifs_dfs_d_automount() {return -EREMOTE} handler when CONFIG_CIFS_DFS_UPCALL is disabled. An alternative would be to avoid flagging S_AUTOMOUNT, etc. without CONFIG_CIFS_DFS_UPCALL. This approach was chosen as it provides more control over the error path.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon Linux Ami 2 | — | Upgrade kernel-debuginfoUpgrade kernel-headersUpgrade perf-debuginfoUpgrade python-perf-debuginfoUpgrade perfUpgrade bpftool-debuginfoUpgrade kernel-tools-debuginfoUpgrade kernel-develUpgrade kernel-livepatch-5.10.177-158.645Upgrade kernel-livepatch-4.14.313-235.533Upgrade kernel-debuginfo-common-x86_64Upgrade kernelUpgrade kernel-tools-develUpgrade bpftoolUpgrade kernel-livepatch-5.15.106-64.140Upgrade kernel-debuginfo-common-aarch64Upgrade python-perfUpgrade kernel-tools | May 20, 2026 | May 20, 2026 |
| Amazon_linux_2023 | — | Upgrade kernel-tools-debuginfoUpgrade kernel-toolsUpgrade python3-perf-debuginfoUpgrade bpftool-debuginfoUpgrade kernel-debuginfoUpgrade kernel-libbpfUpgrade kernel-headersUpgrade kernel-livepatch-6.1.23-36.46Upgrade bpftoolUpgrade kernel-debuginfo-common-x86_64Upgrade kernel-tools-develUpgrade kernel-libbpf-develUpgrade kernel-develUpgrade perf-debuginfoUpgrade python3-perfUpgrade kernel-debuginfo-common-aarch64Upgrade kernelUpgrade perfUpgrade kernel-libbpf-static | Oct 16, 2025 | Sep 15, 2025 |
| Debian | — | Upgrade linux | Sep 17, 2025 | Sep 17, 2025 |
| Huawei Euleros 2_0_sp13 | — | Upgrade kernel-tools-libsUpgrade kernel-abi-stablelistsUpgrade bpftoolUpgrade kernel-toolsUpgrade kernelUpgrade python3-perf | Mar 10, 2026 | Mar 10, 2026 |
| Redhat_linux | — | No solution exists | Jul 17, 2026 | Sep 15, 2025 |
| Ubuntu | — | Upgrade linux-gkeopUpgrade linux-fipsUpgrade linux-nvidiaUpgrade linux-lowlatency-hwe-5.15Upgrade linux-gcpUpgrade linux-aws-5.15Upgrade linux-oracle-5.4Upgrade linux-lowlatencyUpgrade linux-azure-5.15Upgrade linux-nvidia-tegraUpgrade linux-ibm-5.15Upgrade linux-intel-iot-realtimeUpgrade linux-raspiUpgrade linux-oracleUpgrade linux-azure-fdeUpgrade linux-kvmUpgrade linux-riscv-5.15Upgrade linux-nvidia-tegra-5.15Upgrade linux-ibm-5.4Upgrade linux-gkeUpgrade linux-azure-fde-5.15Upgrade linux-xilinx-zynqmpUpgrade linux-oracle-5.15Upgrade linux-aws-5.4Upgrade linux-intel-iotgUpgrade linux-azure-fipsUpgrade linux-aws-fipsUpgrade linuxUpgrade linux-raspi-5.4Upgrade linux-hwe-5.15Upgrade linux-azureUpgrade linux-nvidia-tegra-igxUpgrade linux-awsUpgrade linux-gcp-5.15Upgrade linux-gcp-5.4Upgrade linux-ibmUpgrade linux-bluefieldUpgrade linux-iotUpgrade linux-hwe-5.4Upgrade linux-intel-iotg-5.15Upgrade linux-gcp-fipsUpgrade linux-realtimeUpgrade linux-azure-5.4 | Sep 19, 2025 | Sep 16, 2025 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Oct 15, 2025 | Sep 15, 2025 |
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