CRITICAL
dcache HashTable OOB
CVE-2026-43071
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
KernelScan AI4.4MEDIUM
01Description
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.
02KernelScan AI Analysis
Risk summary
Attackers with root privileges (or equivalent boot configuration access) can trigger a kernel panic by configuring the dhash_entries boot parameter to 1, causing an out-of-bounds read in the dentry hash table during subsequent dcache lookups. This results in immediate system unavailability but does not compromise data integrity or confidentiality.
Vulnerability analysis
The vulnerability occurs when dhash_entries=1 is set as a kernel boot parameter, creating a dentry hash table with only one bucket and setting d_hash_shift to 32. During hash lookups, the expression ((u32)hashlen >> d_hash_shift) exhibits undefined behavior because right-shifting by 32 bits on a 32-bit value is undefined in C, effectively becoming hashlen itself. This causes the hash function to access unallocated memory beyond the single allocated bucket, triggering an out-of-bounds read and kernel panic. The fix limits the minimum bucket count to 2, ensuring d_hash_shift never exceeds the bit width of u32.
03Fix Versions
| Branch | Fixed in | Patch commit |
|---|---|---|
| 3.11 | 3.11 | 45b06bb5ea96 |
| 3.13 | 3.13 | 426ef05e82ee |
| 3.15 | 3.15 | ddd57ebce245 |
| 3.17 | 3.17 | 755b40903eff |
| 6.1 | 6.1.175 | 5718df131ab7 |
| 6.12 | 6.12.83 | f08fe8891c3e |
| 6.18 | 6.18.24 | — |
| 6.19 | 6.19.14 | — |
| 6.6 | 6.6.136 | 277cedabb0ab |
| 7.0 | 7.0.1 | — |
| mainline | 7.1-rc1 | — |