{"id":"CVE-2026-98942","state":"PUBLISHED","title":"sched_ext: Build the cid tables privately and publish them with RCU","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Build the cid tables privately and publish them with RCU\n\nThe cid tables are visible to the cid kfuncs while being modified: the\nfirst enable publishes the global pointers before filling them,\nops.init_cids() overrides rewrite them in place, and re-enables rebuild\nthem in place. A racing TRACING or SYSCALL program can read unfilled\nentries, including uninitialized memory in the kmalloc'd tables, or torn\ntopo updates.\n\nTie the tables' lifetimes to the root sched instead: each root enable\nbuilds a fresh set privately and publishes the per-table __rcu globals once\nthe layout is final, and root disable unpublishes and RCU-frees the set. A\nnon-NULL global is now always a fully built table which stays valid for the\nreader's RCU read section, and lookups stay two loads. Kfuncs treat NULL as\nno-mapping, also after the scheduler exits instead of reporting the stale\nlast mapping.\n\nThe cid kfuncs are available whether the root scheduler is cid-form or\ncpu-form, the latter to allow gradual migration to cids. Every root\ntherefore builds and publishes a default mapping.\n\nEvery reader must either be gated on scheduler liveness or NULL-check\ninside an RCU read section. Fix the two kfuncs that were neither:\nscx_bpf_this_cid() read the table with no RCU or preemption protection and\nscx_bpf_task_cid() relied on KF_RCU, which doesn't put a sleepable program\nin an RCU read section. The hotplug callbacks are instead serialized by\nretiring the tables inside the cpus_read_lock() section that clears\nscx_root.\n\nv2: Document why every root builds the tables (desc + cid.c comment).","publishedAt":"2026-10-23T12:12:14.180Z","updatedAt":"2026-10-26T06:56:52.637Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e9b55af47edf6e60c9a47b5604c3e15c5162ec86","status":"affected","lessThan":"0e1a74369bdbc357d3d9713734418d914a981553","versionType":"git"},{"version":"e9b55af47edf6e60c9a47b5604c3e15c5162ec86","status":"affected","lessThan":"3a773220d39ba993dfe5d135f8b610be10794d5d","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/sched/ext/cid.c","kernel/sched/ext/cid.h","kernel/sched/ext/ext.c","kernel/sched/ext/internal.h","kernel/sched/ext/sub.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.2","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.2","versionType":"semver"},{"version":"7.2.10","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/sched/ext/cid.c","kernel/sched/ext/cid.h","kernel/sched/ext/ext.c","kernel/sched/ext/internal.h","kernel/sched/ext/sub.c"]}],"references":["https://git.kernel.org/stable/c/0e1a74369bdbc357d3d9713734418d914a981553","https://git.kernel.org/stable/c/3a773220d39ba993dfe5d135f8b610be10794d5d"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98942.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98942","state":"PUBLISHED","datePublished":"2026-10-23T12:12:14.180Z","dateUpdated":"2026-10-26T06:56:52.637Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.381Z"},"containers":{"cna":{"title":"sched_ext: Build the cid tables privately and publish them with RCU","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Build the cid tables privately and publish them with RCU\n\nThe cid tables are visible to the cid kfuncs while being modified: the\nfirst enable publishes the global pointers before filling them,\nops.init_cids() overrides rewrite them in place, and re-enables rebuild\nthem in place. A racing TRACING or SYSCALL program can read unfilled\nentries, including uninitialized memory in the kmalloc'd tables, or torn\ntopo updates.\n\nTie the tables' lifetimes to the root sched instead: each root enable\nbuilds a fresh set privately and publishes the per-table __rcu globals once\nthe layout is final, and root disable unpublishes and RCU-frees the set. A\nnon-NULL global is now always a fully built table which stays valid for the\nreader's RCU read section, and lookups stay two loads. Kfuncs treat NULL as\nno-mapping, also after the scheduler exits instead of reporting the stale\nlast mapping.\n\nThe cid kfuncs are available whether the root scheduler is cid-form or\ncpu-form, the latter to allow gradual migration to cids. Every root\ntherefore builds and publishes a default mapping.\n\nEvery reader must either be gated on scheduler liveness or NULL-check\ninside an RCU read section. Fix the two kfuncs that were neither:\nscx_bpf_this_cid() read the table with no RCU or preemption protection and\nscx_bpf_task_cid() relied on KF_RCU, which doesn't put a sleepable program\nin an RCU read section. The hotplug callbacks are instead serialized by\nretiring the tables inside the cpus_read_lock() section that clears\nscx_root.\n\nv2: Document why every root builds the tables (desc + cid.c comment)."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e9b55af47edf6e60c9a47b5604c3e15c5162ec86","status":"affected","lessThan":"0e1a74369bdbc357d3d9713734418d914a981553","versionType":"git"},{"version":"e9b55af47edf6e60c9a47b5604c3e15c5162ec86","status":"affected","lessThan":"3a773220d39ba993dfe5d135f8b610be10794d5d","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/sched/ext/cid.c","kernel/sched/ext/cid.h","kernel/sched/ext/ext.c","kernel/sched/ext/internal.h","kernel/sched/ext/sub.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.2","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.2","versionType":"semver"},{"version":"7.2.10","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/sched/ext/cid.c","kernel/sched/ext/cid.h","kernel/sched/ext/ext.c","kernel/sched/ext/internal.h","kernel/sched/ext/sub.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/0e1a74369bdbc357d3d9713734418d914a981553"},{"url":"https://git.kernel.org/stable/c/3a773220d39ba993dfe5d135f8b610be10794d5d"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-26T06:56:52.637Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.2","versionEndExcluding":"7.2.10"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.2","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}