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CVE-2026-99174— ext4: free the sbi after a grace period

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Linux 内核中，以下漏洞已得到修复： ext4：在等待一个 RCU 宽限期（grace period）后再释放 sbi 函数在 RCU 路径遍历（pathwalk）模式下，通过 读取一个符号链接的目标数据块。该过程会在 的 中以及随后的 中读取 ，同时， 还会通过 更新扩展状态（extent status）的命中或未命中计数器。 然而， 在销毁这些计数器、清空 并释放 （superblock info）结构时，并未等待 RCU 宽限期。如果此时仍有路径遍历操作停留在 中（即最后一个对挂载点的引用刚刚消失），

AI Predicted 7.8 Difficulty: Hard

Possible ATT&CK Techniques 1 AI

T1069 · Permission Groups Discovery

Affected Version Matrix 8

VendorProduct Version RangeStatus
Linux Linux 6493792d3299b3e33f887ef8a150099d271faf9c< 80d5db1686b05fad6f384be017714297d828a714 affected
6493792d3299b3e33f887ef8a150099d271faf9c< 87d29b8b849738d52fe820d495fa0aa2d5a1ec82 affected
6493792d3299b3e33f887ef8a150099d271faf9c< c17b44266a1f9fcb49b894d4611d1254bf1aa313 affected
5.19 affected
< 5.19 unaffected
6.18.59≤ 6.18.* unaffected
7.2.13≤ 7.2.* unaffected
7.3≤ * unaffected
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I. Basic Information for CVE-2026-99174

Vulnerability Information
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Vulnerability Title
ext4: free the sbi after a grace period
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: ext4: free the sbi after a grace period ext4_get_link() follows a symlink that keeps its target in a data block in rcu pathwalk mode with ext4_getblk(EXT4_GET_BLOCKS_CACHED_NOWAIT). That reads s_mount_state in the ASSERT() of ext4_getblk() and again in ext4_es_lookup_extent(), and the lookup bumps the extent status hit or miss counter, all through sb->s_fs_info. ext4_put_super() destroys those counters, clears sb->s_fs_info and frees the sbi without waiting for a grace period. A pathwalk that is still in ext4_get_link() when the last reference to the mount goes away then dereferences a NULL s_fs_info, the freed sbi or the destroyed percpu counters. With a pathwalk held up in ext4_get_link() while the last reference goes away: KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af] RIP: 0010:ext4_getblk+0xf0/0x640 Call Trace: <TASK> ext4_get_link+0x26c/0x410 pick_link+0xf96/0x1780 step_into_slowpath+0x9b8/0x1250 path_lookupat+0x484/0xb00 filename_lookup+0x1f1/0x5b0 vfs_statx+0xd7/0x3b0 vfs_fstatat+0x4d/0x90 __do_sys_newfstatat+0xa0/0x100 do_syscall_64+0x10e/0x5e0 entry_SYSCALL_64_after_hwframe+0x77/0x7f So far that has been hard to hit. umount(2) waits for a grace period in namespace_unlock() before it drops the mount, so only a mount whose last reference goes away elsewhere, like the close of a file or a chdir out of a lazily unmounted directory, can race a walker. Keep sb->s_fs_info and free the sbi together with the extent status counters after a grace period. Split the counters out of ext4_es_unregister_shrinker() for that. The shrinker still gets wasted in ext4_put_super(), the counters go with the sbi.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 6493792d3299b3e33f887ef8a150099d271faf9c ~ 80d5db1686b05fad6f384be017714297d828a714 -
Linux Linux 5.19 -

II. Public POCs for CVE-2026-99174

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III. Intelligence Information for CVE-2026-99174

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Patches & Fixes for CVE-2026-99174 (3)

Same Patch Batch · Linux · 2026-10-28 · 117 CVEs total

CVE-2026-99143 tracing: Keep the predicate limit separate from program capacity
CVE-2026-99129 selinux: fix BPF token permission checks
CVE-2026-99130 io_uring/cancel: don't spin on local work the task can't run
CVE-2026-99131 xfs: fix capability check in xfs
CVE-2026-99133 net/iucv: fix the recvmsg window update
CVE-2026-99132 xfs: don't hold buffer locks across sync transaction commit in xfs_sync_sb_buf
CVE-2026-99134 mac802154: fix data race and NULL deref on local->assoc_dev
CVE-2026-99135 dm-integrity: fix infinite loop on discard with large tag size
CVE-2026-99137 cifs: don't update i_size in cifs_do_truncate without a cached handle
CVE-2026-99136 dm-crypt: fix a tiny race condition in crypt_dec_pending
CVE-2026-99138 tcp: fix use-after-free in do_tcp_getsockopt(TCP_CC_INFO)
CVE-2026-99140 tracing: Fix hist trigger timestamps for buffered events
CVE-2026-99139 tcp: fix use-after-free in do_tcp_getsockopt(TCP_CONGESTION)
CVE-2026-99141 tracing: Fix crash in print_graph_function_event()
CVE-2026-99142 tracing: Check operator stack capacity before pushing
CVE-2026-99154 scsi: libiscsi: Reject a negative task index from parse_pdu_itt
CVE-2026-99151 drm/amd/display: Fix NULL sink dereference in USB4 bandwidth functions
CVE-2026-99153 scsi: libiscsi: Validate the ITT reflected in a Reject PDU
CVE-2026-99152 scsi: libiscsi: Validate the task named by a management response
CVE-2026-99150 drm/amdgpu: don't drop the runtime PM reference twice in amdgpu_gpr

Showing top 20 of 117 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux