{"id":"CVE-2026-74342","state":"PUBLISHED","title":"kernfs: link kn to its parent before the LSM init hook","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nkernfs: link kn to its parent before the LSM init hook\n\nAfter commit 12e9e3cd03b5 (\"simpe_xattr: use per-sb cache\"),\nkernfs_xattr_set() and kernfs_xattr_get() compute the cache via\nkernfs_root(kn) before any other check.  kernfs_root(kn) walks\nkn->__parent first and falls back to kn->dir.root, both of which are\nNULL on a freshly kmem_cache_zalloc()'d kn. kn->__parent was being set\nin kernfs_new_node() after __kernfs_new_node() returned, and kn->dir.root\nis set even later by kernfs_create_dir_ns() / kernfs_create_empty_dir().\n\nThe LSM kernfs_init_security hook is invoked from inside\n__kernfs_new_node(), before either field has been initialized.\nselinux_kernfs_init_security() ends with kernfs_xattr_set(kn,\nXATTR_NAME_SELINUX, ...).  kernfs_root(kn) then returns NULL, and\n&((struct kernfs_root *)NULL)->xa_cache evaluates to\noffsetof(struct kernfs_root, xa_cache) which faults:\n\n  BUG: kernel NULL pointer dereference, address: 00000000000000e0\n  RIP: 0010:simple_xattr_set+0x27/0x8b0\n  Call Trace:\n   kernfs_xattr_set+0x63/0xb0\n   selinux_kernfs_init_security+0x13b/0x270\n   security_kernfs_init_security+0x36/0xc0\n   __kernfs_new_node+0x182/0x290\n   kernfs_new_node+0x80/0xc0\n   kernfs_create_dir_ns+0x2b/0xa0\n   cgroup_create+0x116/0x380\n   cgroup_mkdir+0x7c/0x1a0\n\nReproduces deterministically at PID 1 (systemd) on an SELinux-enabled\ndistro. The first cgroup mkdir under /sys/fs/cgroup with a labelled\nparent panics the kernel.\n\nThe LSM hook's contract is that the kn_dir argument is the parent of\nthe new kn, so kn->__parent should already point at kn_dir when the\nhook runs.  Move kernfs_get(parent) and rcu_assign_pointer of\nkn->__parent from kernfs_new_node() into __kernfs_new_node() right\nbefore the security hook, and unwind the parent reference on the\nerr_out4 path.  kernfs_root(kn) then takes its parent branch during\nthe hook and returns parent->dir.root, which is the correct root.\n\nThis also closes the same-shape latent bug in kernfs_xattr_get() (which\ntoday is hidden only by kernfs_iattrs_noalloc() returning NULL on a\nfresh kn).","publishedAt":"2026-08-15T05:58:31.924Z","updatedAt":"2026-08-17T05:17:34.554Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"319b82e8b46edaf557436ad858e734e583f78ec9","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"6cccc49b027c7551ffc1d2532f2ef1922661f3da","versionType":"git"},{"version":"0","status":"affected","lessThan":"7.1.5","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/kernfs/dir.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/kernfs/dir.c"]}],"references":["https://git.kernel.org/stable/c/319b82e8b46edaf557436ad858e734e583f78ec9","https://git.kernel.org/stable/c/6cccc49b027c7551ffc1d2532f2ef1922661f3da"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/74xxx/CVE-2026-74342.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-74342","state":"PUBLISHED","datePublished":"2026-08-15T05:58:31.924Z","dateUpdated":"2026-08-17T05:17:34.554Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-15T05:44:03.886Z"},"containers":{"cna":{"title":"kernfs: link kn to its parent before the LSM init hook","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nkernfs: link kn to its parent before the LSM init hook\n\nAfter commit 12e9e3cd03b5 (\"simpe_xattr: use per-sb cache\"),\nkernfs_xattr_set() and kernfs_xattr_get() compute the cache via\nkernfs_root(kn) before any other check.  kernfs_root(kn) walks\nkn->__parent first and falls back to kn->dir.root, both of which are\nNULL on a freshly kmem_cache_zalloc()'d kn. kn->__parent was being set\nin kernfs_new_node() after __kernfs_new_node() returned, and kn->dir.root\nis set even later by kernfs_create_dir_ns() / kernfs_create_empty_dir().\n\nThe LSM kernfs_init_security hook is invoked from inside\n__kernfs_new_node(), before either field has been initialized.\nselinux_kernfs_init_security() ends with kernfs_xattr_set(kn,\nXATTR_NAME_SELINUX, ...).  kernfs_root(kn) then returns NULL, and\n&((struct kernfs_root *)NULL)->xa_cache evaluates to\noffsetof(struct kernfs_root, xa_cache) which faults:\n\n  BUG: kernel NULL pointer dereference, address: 00000000000000e0\n  RIP: 0010:simple_xattr_set+0x27/0x8b0\n  Call Trace:\n   kernfs_xattr_set+0x63/0xb0\n   selinux_kernfs_init_security+0x13b/0x270\n   security_kernfs_init_security+0x36/0xc0\n   __kernfs_new_node+0x182/0x290\n   kernfs_new_node+0x80/0xc0\n   kernfs_create_dir_ns+0x2b/0xa0\n   cgroup_create+0x116/0x380\n   cgroup_mkdir+0x7c/0x1a0\n\nReproduces deterministically at PID 1 (systemd) on an SELinux-enabled\ndistro. The first cgroup mkdir under /sys/fs/cgroup with a labelled\nparent panics the kernel.\n\nThe LSM hook's contract is that the kn_dir argument is the parent of\nthe new kn, so kn->__parent should already point at kn_dir when the\nhook runs.  Move kernfs_get(parent) and rcu_assign_pointer of\nkn->__parent from kernfs_new_node() into __kernfs_new_node() right\nbefore the security hook, and unwind the parent reference on the\nerr_out4 path.  kernfs_root(kn) then takes its parent branch during\nthe hook and returns parent->dir.root, which is the correct root.\n\nThis also closes the same-shape latent bug in kernfs_xattr_get() (which\ntoday is hidden only by kernfs_iattrs_noalloc() returning NULL on a\nfresh kn)."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"319b82e8b46edaf557436ad858e734e583f78ec9","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"6cccc49b027c7551ffc1d2532f2ef1922661f3da","versionType":"git"},{"version":"0","status":"affected","lessThan":"7.1.5","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/kernfs/dir.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/kernfs/dir.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/319b82e8b46edaf557436ad858e734e583f78ec9"},{"url":"https://git.kernel.org/stable/c/6cccc49b027c7551ffc1d2532f2ef1922661f3da"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-17T05:17:34.554Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}