CVE-2026-43071dcache: Limit the minimal number of bucket to two

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/45b06bb5ea96f75ad81d7ef446f832ea6b0026fe
• https://git.kernel.org/stable/c/426ef05e82ee52c8d0e95fc0808b7383d8352d73
• https://git.kernel.org/stable/c/ddd57ebce245f9c7e2f6902a6c087d6186d2385d
• https://git.kernel.org/stable/c/755b40903eff563768d4d96fd4ef51ec48adde3b
• https://git.kernel.org/stable/c/5718df131ab78897a9dd1f2e71c3ba732d4392af
• https://git.kernel.org/stable/c/277cedabb0ab86baae83fa58218be13c6d3e5526
• https://git.kernel.org/stable/c/f08fe8891c3eeb63b73f9f1f6d97aa629c821579
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html