{"id":"CVE-2021-46988","state":"PUBLISHED","title":"userfaultfd: release page in error path to avoid BUG_ON","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nuserfaultfd: release page in error path to avoid BUG_ON\n\nConsider the following sequence of events:\n\n1. Userspace issues a UFFD ioctl, which ends up calling into\n   shmem_mfill_atomic_pte(). We successfully account the blocks, we\n   shmem_alloc_page(), but then the copy_from_user() fails. We return\n   -ENOENT. We don't release the page we allocated.\n2. Our caller detects this error code, tries the copy_from_user() after\n   dropping the mmap_lock, and retries, calling back into\n   shmem_mfill_atomic_pte().\n3. Meanwhile, let's say another process filled up the tmpfs being used.\n4. So shmem_mfill_atomic_pte() fails to account blocks this time, and\n   immediately returns - without releasing the page.\n\nThis triggers a BUG_ON in our caller, which asserts that the page\nshould always be consumed, unless -ENOENT is returned.\n\nTo fix this, detect if we have such a \"dangling\" page when accounting\nfails, and if so, release it before returning.","publishedAt":"2024-02-28T08:13:15.310Z","updatedAt":"2026-05-11T13:45:47.021Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"319116227e52d49eee671f0aa278bac89b3c1b69","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"140cfd9980124aecb6c03ef2e69c72d0548744de","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"ad53127973034c63b5348715a1043d0e80ceb330","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"2d59a0ed8b26b8f3638d8afc31f839e27759f1f6","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"7ed9d238c7dbb1fdb63ad96a6184985151b0171c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/shmem.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.11","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.11","versionType":"semver"},{"version":"4.14.233","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.191","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.120","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.38","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.11.22","status":"unaffected","lessThanOrEqual":"5.11.*","versionType":"semver"},{"version":"5.12.5","status":"unaffected","lessThanOrEqual":"5.12.*","versionType":"semver"},{"version":"5.13","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/shmem.c"]}],"references":["https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69","https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f","https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43","https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744de","https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330","https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6","https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171c"],"weaknesses":[],"ingestedAt":"2026-10-29T19:49:16.371Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/46xxx/CVE-2021-46988.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-46988","state":"PUBLISHED","datePublished":"2024-02-28T08:13:15.310Z","dateUpdated":"2026-05-11T13:45:47.021Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-02-27T18:42:55.948Z"},"containers":{"cna":{"title":"userfaultfd: release page in error path to avoid BUG_ON","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nuserfaultfd: release page in error path to avoid BUG_ON\n\nConsider the following sequence of events:\n\n1. Userspace issues a UFFD ioctl, which ends up calling into\n   shmem_mfill_atomic_pte(). We successfully account the blocks, we\n   shmem_alloc_page(), but then the copy_from_user() fails. We return\n   -ENOENT. We don't release the page we allocated.\n2. Our caller detects this error code, tries the copy_from_user() after\n   dropping the mmap_lock, and retries, calling back into\n   shmem_mfill_atomic_pte().\n3. Meanwhile, let's say another process filled up the tmpfs being used.\n4. So shmem_mfill_atomic_pte() fails to account blocks this time, and\n   immediately returns - without releasing the page.\n\nThis triggers a BUG_ON in our caller, which asserts that the page\nshould always be consumed, unless -ENOENT is returned.\n\nTo fix this, detect if we have such a \"dangling\" page when accounting\nfails, and if so, release it before returning."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"319116227e52d49eee671f0aa278bac89b3c1b69","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"140cfd9980124aecb6c03ef2e69c72d0548744de","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"ad53127973034c63b5348715a1043d0e80ceb330","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"2d59a0ed8b26b8f3638d8afc31f839e27759f1f6","versionType":"git"},{"version":"cb658a453b9327ce96ce5222c24d162b5b65b564","status":"affected","lessThan":"7ed9d238c7dbb1fdb63ad96a6184985151b0171c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/shmem.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.11","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.11","versionType":"semver"},{"version":"4.14.233","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.191","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.120","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.38","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.11.22","status":"unaffected","lessThanOrEqual":"5.11.*","versionType":"semver"},{"version":"5.12.5","status":"unaffected","lessThanOrEqual":"5.12.*","versionType":"semver"},{"version":"5.13","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/shmem.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69"},{"url":"https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f"},{"url":"https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43"},{"url":"https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744de"},{"url":"https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330"},{"url":"https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6"},{"url":"https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171c"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-11T13:45:47.021Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.11","versionEndExcluding":"4.14.233"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.11","versionEndExcluding":"4.19.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.11","versionEndExcluding":"5.4.120"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.11","versionEndExcluding":"5.10.38"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.11","versionEndExcluding":"5.11.22"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.11","versionEndExcluding":"5.12.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.11","versionEndExcluding":"5.13"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2024-06-21T16:28:01.611692Z","id":"CVE-2021-46988","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2024-06-21T16:28:13.369Z"}},{"title":"CVE Program Container","references":[{"url":"https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744de","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171c","tags":["x_transferred"]}],"providerMetadata":{"shortName":"CVE","orgId":"af854a3a-2127-422b-91ae-364da2661108","dateUpdated":"2024-08-04T05:24:38.475Z"}}]}}}