{"id":"CVE-2026-23319","summary":"bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim\n\nThe root cause of this bug is that when 'bpf_link_put' reduces the\nrefcount of 'shim_link-\u003elink.link' to zero, the resource is considered\nreleased but may still be referenced via 'tr-\u003eprogs_hlist' in\n'cgroup_shim_find'. The actual cleanup of 'tr-\u003eprogs_hlist' in\n'bpf_shim_tramp_link_release' is deferred. During this window, another\nprocess can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'.\n\nBased on Martin KaFai Lau's suggestions, I have created a simple patch.\n\nTo fix this:\n   Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'.\n   Only increment the refcount if it is not already zero.\n\nTesting:\n   I verified the fix by adding a delay in\n   'bpf_shim_tramp_link_release' to make the bug easier to trigger:\n\nstatic void bpf_shim_tramp_link_release(struct bpf_link *link)\n{\n\t/* ... */\n\tif (!shim_link-\u003etrampoline)\n\t\treturn;\n\n+\tmsleep(100);\n\tWARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link-\u003elink,\n\t\tshim_link-\u003etrampoline, NULL));\n\tbpf_trampoline_put(shim_link-\u003etrampoline);\n}\n\nBefore the patch, running a PoC easily reproduced the crash(almost 100%)\nwith a call trace similar to KaiyanM's report.\nAfter the patch, the bug no longer occurs even after millions of\niterations.","modified":"2026-04-02T13:12:21.260026Z","published":"2026-03-25T10:27:13.678Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23319.json","cna_assigner":"Linux"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cff"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23319.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-23319"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e"},{"fixed":"529e685e522b9d7fb379dbe6929dcdf520e34c8c"},{"fixed":"9b02c5c4147f8af8ed783c8deb5df927a55c3951"},{"fixed":"cfcfa0ca0212162aa472551266038e8fd6768cff"},{"fixed":"3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2"},{"fixed":"4e8a0005d633a4adc98e3b65d5080f93b90d356b"},{"fixed":"56145d237385ca0e7ca9ff7b226aaf2eb8ef368b"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23319.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.0.0"},{"fixed":"6.1.167"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.130"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.77"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.17"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.7"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23319.json"}}],"schema_version":"1.7.5"}