mailist inclusion category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/13644 Reference: https://lore.kernel.org/linux-fsdevel/20260130034853.215819-1-chengzhihao1@h... -------------------------------- 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. Fixes: ceb5bdc2d246 ("fs: dcache per-bucket dcache hash locking") Cc: stable@vger.kernel.org Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com> --- fs/dcache.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index e0f476c567b0..ea0154f81497 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -3394,7 +3394,7 @@ static void __init dcache_init_early(void) HASH_EARLY | HASH_ZERO, &d_hash_shift, NULL, - 0, + 2, 0); d_hash_shift = 32 - d_hash_shift; } @@ -3422,7 +3422,7 @@ static void __init dcache_init(void) HASH_ZERO, &d_hash_shift, NULL, - 0, + 2, 0); d_hash_shift = 32 - d_hash_shift; } -- 2.52.0