{"id":"CVE-2026-99174","state":"PUBLISHED","title":"ext4: free the sbi after a grace period","description":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: free the sbi after a grace period\n\next4_get_link() follows a symlink that keeps its target in a data block\nin rcu pathwalk mode with ext4_getblk(EXT4_GET_BLOCKS_CACHED_NOWAIT).\nThat reads s_mount_state in the ASSERT() of ext4_getblk() and again in\next4_es_lookup_extent(), and the lookup bumps the extent status hit or\nmiss counter, all through sb->s_fs_info.\n\next4_put_super() destroys those counters, clears sb->s_fs_info and frees\nthe sbi without waiting for a grace period. A pathwalk that is still in\next4_get_link() when the last reference to the mount goes away then\ndereferences a NULL s_fs_info, the freed sbi or the destroyed percpu\ncounters.\n\nWith a pathwalk held up in ext4_get_link() while the last reference\ngoes away:\n\n  KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af]\n  RIP: 0010:ext4_getblk+0xf0/0x640\n  Call Trace:\n   <TASK>\n   ext4_get_link+0x26c/0x410\n   pick_link+0xf96/0x1780\n   step_into_slowpath+0x9b8/0x1250\n   path_lookupat+0x484/0xb00\n   filename_lookup+0x1f1/0x5b0\n   vfs_statx+0xd7/0x3b0\n   vfs_fstatat+0x4d/0x90\n   __do_sys_newfstatat+0xa0/0x100\n   do_syscall_64+0x10e/0x5e0\n   entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\nSo far that has been hard to hit. umount(2) waits for a grace period in\nnamespace_unlock() before it drops the mount, so only a mount whose last\nreference goes away elsewhere, like the close of a file or a chdir out of\na lazily unmounted directory, can race a walker.\n\nKeep sb->s_fs_info and free the sbi together with the extent status\ncounters after a grace period. Split the counters out of\next4_es_unregister_shrinker() for that. The shrinker still gets wasted\nin ext4_put_super(), the counters go with the sbi.","publishedAt":"2026-10-28T10:35:28.758Z","updatedAt":"2026-10-30T12:42:37.969Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"cf3bd5824c985b350d150bcd76698ee5e993fcba","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"b4b0598fad51a978fcbda9d55eef6b5bd3cbe7d8","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"4ce0e27ea610663a9cdc04e3bca38559147428d4","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"80d5db1686b05fad6f384be017714297d828a714","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"87d29b8b849738d52fe820d495fa0aa2d5a1ec82","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"c17b44266a1f9fcb49b894d4611d1254bf1aa313","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/ext4.h","fs/ext4/extents-test.c","fs/ext4/extents.c","fs/ext4/extents_status.c","fs/ext4/extents_status.h","fs/ext4/super.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.19","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.161","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.115","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.59","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.13","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":["fs/ext4/ext4.h","fs/ext4/extents-test.c","fs/ext4/extents.c","fs/ext4/extents_status.c","fs/ext4/extents_status.h","fs/ext4/super.c"]}],"references":["https://git.kernel.org/stable/c/cf3bd5824c985b350d150bcd76698ee5e993fcba","https://git.kernel.org/stable/c/b4b0598fad51a978fcbda9d55eef6b5bd3cbe7d8","https://git.kernel.org/stable/c/4ce0e27ea610663a9cdc04e3bca38559147428d4","https://git.kernel.org/stable/c/80d5db1686b05fad6f384be017714297d828a714","https://git.kernel.org/stable/c/87d29b8b849738d52fe820d495fa0aa2d5a1ec82","https://git.kernel.org/stable/c/c17b44266a1f9fcb49b894d4611d1254bf1aa313"],"weaknesses":[],"ingestedAt":"2026-10-30T13:02:04.640Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/99xxx/CVE-2026-99174.json","commit":"cb14bf1b43b0c9f05f7f40eae2246263fd430780","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-99174","state":"PUBLISHED","datePublished":"2026-10-28T10:35:28.758Z","dateUpdated":"2026-10-30T12:42:37.969Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.399Z"},"containers":{"cna":{"title":"ext4: free the sbi after a grace period","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: free the sbi after a grace period\n\next4_get_link() follows a symlink that keeps its target in a data block\nin rcu pathwalk mode with ext4_getblk(EXT4_GET_BLOCKS_CACHED_NOWAIT).\nThat reads s_mount_state in the ASSERT() of ext4_getblk() and again in\next4_es_lookup_extent(), and the lookup bumps the extent status hit or\nmiss counter, all through sb->s_fs_info.\n\next4_put_super() destroys those counters, clears sb->s_fs_info and frees\nthe sbi without waiting for a grace period. A pathwalk that is still in\next4_get_link() when the last reference to the mount goes away then\ndereferences a NULL s_fs_info, the freed sbi or the destroyed percpu\ncounters.\n\nWith a pathwalk held up in ext4_get_link() while the last reference\ngoes away:\n\n  KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af]\n  RIP: 0010:ext4_getblk+0xf0/0x640\n  Call Trace:\n   <TASK>\n   ext4_get_link+0x26c/0x410\n   pick_link+0xf96/0x1780\n   step_into_slowpath+0x9b8/0x1250\n   path_lookupat+0x484/0xb00\n   filename_lookup+0x1f1/0x5b0\n   vfs_statx+0xd7/0x3b0\n   vfs_fstatat+0x4d/0x90\n   __do_sys_newfstatat+0xa0/0x100\n   do_syscall_64+0x10e/0x5e0\n   entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\nSo far that has been hard to hit. umount(2) waits for a grace period in\nnamespace_unlock() before it drops the mount, so only a mount whose last\nreference goes away elsewhere, like the close of a file or a chdir out of\na lazily unmounted directory, can race a walker.\n\nKeep sb->s_fs_info and free the sbi together with the extent status\ncounters after a grace period. Split the counters out of\next4_es_unregister_shrinker() for that. The shrinker still gets wasted\nin ext4_put_super(), the counters go with the sbi."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"cf3bd5824c985b350d150bcd76698ee5e993fcba","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"b4b0598fad51a978fcbda9d55eef6b5bd3cbe7d8","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"4ce0e27ea610663a9cdc04e3bca38559147428d4","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"80d5db1686b05fad6f384be017714297d828a714","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"87d29b8b849738d52fe820d495fa0aa2d5a1ec82","versionType":"git"},{"version":"6493792d3299b3e33f887ef8a150099d271faf9c","status":"affected","lessThan":"c17b44266a1f9fcb49b894d4611d1254bf1aa313","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/ext4.h","fs/ext4/extents-test.c","fs/ext4/extents.c","fs/ext4/extents_status.c","fs/ext4/extents_status.h","fs/ext4/super.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.19","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.161","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.115","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.59","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.13","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":["fs/ext4/ext4.h","fs/ext4/extents-test.c","fs/ext4/extents.c","fs/ext4/extents_status.c","fs/ext4/extents_status.h","fs/ext4/super.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/cf3bd5824c985b350d150bcd76698ee5e993fcba"},{"url":"https://git.kernel.org/stable/c/b4b0598fad51a978fcbda9d55eef6b5bd3cbe7d8"},{"url":"https://git.kernel.org/stable/c/4ce0e27ea610663a9cdc04e3bca38559147428d4"},{"url":"https://git.kernel.org/stable/c/80d5db1686b05fad6f384be017714297d828a714"},{"url":"https://git.kernel.org/stable/c/87d29b8b849738d52fe820d495fa0aa2d5a1ec82"},{"url":"https://git.kernel.org/stable/c/c17b44266a1f9fcb49b894d4611d1254bf1aa313"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:42:37.969Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.19","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.19","versionEndExcluding":"6.6.161"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.19","versionEndExcluding":"6.12.115"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.19","versionEndExcluding":"6.18.59"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.19","versionEndExcluding":"7.2.13"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.19","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}