{"id":"AZL-111326","summary":"CVE-2026-99174 affecting package kernel 6.6.157.1-1","details":"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-\u003es_fs_info.\n\next4_put_super() destroys those counters, clears sb-\u003es_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   \u003cTASK\u003e\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-\u003es_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.","modified":"2026-10-30T05:35:37Z","published":"2026-10-28T11:17:38Z","upstream":["CVE-2026-99174"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99174"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.157.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-111326.json"}}],"schema_version":"1.9.2"}