UBUNTU-CVE-2026-43071

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UBUNTU-CVE-2026-43071

Summary:

Details: 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' won't exceeds the bit width of type u32.

References: https://ubuntu.com/security/CVE-2026-43071, https://www.cve.org/CVERecord?id=CVE-2026-43071, https://git.kernel.org/linus/f08fe8891c3eeb63b73f9f1f6d97aa629c821579, https://ubuntu.com/security/notices/USN-8488-1, https://ubuntu.com/security/notices/USN-8490-1, https://ubuntu.com/security/notices/USN-8491-1, https://ubuntu.com/security/notices/USN-8492-1, https://ubuntu.com/security/notices/USN-8493-1, https://ubuntu.com/security/notices/USN-8488-2, https://ubuntu.com/security/notices/USN-8492-2, https://ubuntu.com/security/notices/USN-8497-1, https://ubuntu.com/security/notices/USN-8498-1, https://ubuntu.com/security/notices/USN-8499-1, https://ubuntu.com/security/notices/USN-8493-2, https://ubuntu.com/security/notices/USN-8507-1, https://ubuntu.com/security/notices/USN-8508-1, https://ubuntu.com/security/notices/USN-8492-3, https://ubuntu.com/security/notices/USN-8490-2, https://ubuntu.com/security/notices/USN-8492-4, https://ubuntu.com/security/notices/USN-8492-5, https://ubuntu.com/security/notices/USN-8527-1, https://ubuntu.com/security/notices/USN-8528-1, https://ubuntu.com/security/notices/USN-8545-1, https://ubuntu.com/security/notices/USN-8546-1, https://ubuntu.com/security/notices/USN-8547-1, https://ubuntu.com/security/notices/USN-8569-1, https://ubuntu.com/security/notices/USN-8603-1, https://ubuntu.com/security/notices/USN-8604-1, https://ubuntu.com/security/notices/USN-8605-1, https://ubuntu.com/security/notices/USN-8606-1, https://ubuntu.com/security/notices/USN-8607-1, https://ubuntu.com/security/notices/USN-8609-1, https://ubuntu.com/security/notices/USN-8547-2, https://ubuntu.com/security/notices/USN-8619-1, https://ubuntu.com/security/notices/USN-8644-1, https://ubuntu.com/security/notices/USN-8645-1, https://ubuntu.com/security/notices/USN-8644-2, https://ubuntu.com/security/notices/USN-8666-1, https://ubuntu.com/security/notices/USN-8667-1, https://ubuntu.com/security/notices/USN-8666-2, https://ubuntu.com/security/notices/USN-8644-3, https://ubuntu.com/security/notices/USN-8666-3, https://ubuntu.com/security/notices/USN-8715-1, https://ubuntu.com/security/notices/USN-8725-1