CVE-2026-43071

In the Linux kernel, the following vulnerability has been resolved:

dcache: Limit the minimal number of bucket to two

There is an OOB read problem on dentry_hashtable when user sets dhash_entries=1: BUG: unable to handle page fault for address: ffff888b30b774b0 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page Oops: Oops: 0000 [#1] SMP PTI RIP: 0010:__d_lookup+0x56/0x120 Call Trace: d_lookup.cold+0x16/0x5d lookup_dcache+0x27/0xf0 lookup_one_qstr_excl+0x2a/0x180 start_dirop+0x55/0xa0 simple_start_creating+0x8d/0xa0 debugfs_start_creating+0x8c/0x180 debugfs_create_dir+0x1d/0x1c0 pinctrl_init+0x6d/0x140 do_one_initcall+0x6d/0x3d0 kernel_init_freeable+0x39f/0x460 kernel_init+0x2a/0x260

There will be only one bucket in dentry_hashtable when dhash_entries is set as one, and d_hash_shift is calculated as 32 by dcache_init(). Then, following process will access more than one buckets(which memory region is not allocated) in dentry_hashtable: d_lookup b = d_hash(hash) dentry_hashtable + ((u32)hashlen » d_hash_shift) // The C standard defines the behavior of right shift amounts // exceeding the bit width of the operand as undefined. The // result of (u32)hashlen » d_hash_shift becomes hashlen, // so b will point to an unallocated memory region. hlist_bl_for_each_entry_rcu(b) hlist_bl_first_rcu(head) h->first // read OOB!

Fix it by limiting the minimal number of dentry_hashtable bucket to two, so that d_hash_shift wont exceeds the bit width of type u32.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/277cedabb0ab86baae83fa58218be13c6d3e5526
• https://git.kernel.org/stable/c/426ef05e82ee52c8d0e95fc0808b7383d8352d73
• https://git.kernel.org/stable/c/45b06bb5ea96f75ad81d7ef446f832ea6b0026fe
• https://git.kernel.org/stable/c/5718df131ab78897a9dd1f2e71c3ba732d4392af
• https://git.kernel.org/stable/c/755b40903eff563768d4d96fd4ef51ec48adde3b
• https://git.kernel.org/stable/c/ddd57ebce245f9c7e2f6902a6c087d6186d2385d
• https://git.kernel.org/stable/c/f08fe8891c3eeb63b73f9f1f6d97aa629c821579