CVE-2025-38263

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

bcache: fix NULL pointer in cache_set_flush()

1. LINE#1794 - LINE#1887 is some codes about function of bch_cache_set_alloc().
2. LINE#2078 - LINE#2142 is some codes about function of register_cache_set().
3. register_cache_set() will call bch_cache_set_alloc() in LINE#2098.

1794 struct cache_set *bch_cache_set_alloc(struct cache_sb *sb) 1795 { … 1860 if (!(c->devices = kcalloc(c->nr_uuids, sizeof(void *), GFP_KERNEL)) || 1861 mempool_init_slab_pool(&c->search, 32, bch_search_cache) || 1862 mempool_init_kmalloc_pool(&c->bio_meta, 2, 1863 sizeof(struct bbio) + sizeof(struct bio_vec) * 1864 bucket_pages(c)) || 1865 mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size) || 1866 bioset_init(&c->bio_split, 4, offsetof(struct bbio, bio), 1867 BIOSET_NEED_BVECS|BIOSET_NEED_RESCUER) || 1868 !(c->uuids = alloc_bucket_pages(GFP_KERNEL, c)) || 1869 !(c->moving_gc_wq = alloc_workqueue(bcache_gc, 1870 WQ_MEM_RECLAIM, 0)) || 1871 bch_journal_alloc(c) || 1872 bch_btree_cache_alloc(c) || 1873 bch_open_buckets_alloc(c) || 1874 bch_bset_sort_state_init(&c->sort, ilog2(c->btree_pages))) 1875 goto err; ^^^^^^^^ 1876 … 1883 return c; 1884 err: 1885 bch_cache_set_unregister(c); ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1886 return NULL; 1887 } … 2078 static const char *register_cache_set(struct cache *ca) 2079 { … 2098 c = bch_cache_set_alloc(&ca->sb); 2099 if (!c) 2100 return err; ^^^^^^^^^^ … 2128 ca->set = c; 2129 ca->set->cache[ca->sb.nr_this_dev] = ca; ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ … 2138 return NULL; 2139 err: 2140 bch_cache_set_unregister(c); 2141 return err; 2142 }

(1) If LINE#1860 - LINE#1874 is true, then do goto err(LINE#1875) and call bch_cache_set_unregister()(LINE#1885). (2) As (1) return NULL(LINE#1886), LINE#2098 - LINE#2100 would return. (3) As (2) has returned, LINE#2128 - LINE#2129 would do not give the value to c->cache[], it means that c->cache[] is NULL.

LINE#1624 - LINE#1665 is some codes about function of cache_set_flush(). As (1), in LINE#1885 call bch_cache_set_unregister() —> bch_cache_set_stop() —> closure_queue() -.-> cache_set_flush() (as below LINE#1624)

1624 static void cache_set_flush(struct closure *cl) 1625 { … 1654 for_each_cache(ca, c, i) 1655 if (ca->alloc_thread) ^^ 1656 kthread_stop(ca->alloc_thread); … 1665 }

(4) In LINE#1655 ca is NULL(see (3)) in cache_set_flush() then the kernel crash occurred as below: [ 846.712887] bcache: register_cache() error drbd6: cannot allocate memory [ 846.713242] bcache: register_bcache() error : failed to register device [ 846.713336] bcache: cache_set_free() Cache set 2f84bdc1-498a-4f2f-98a7-01946bf54287 unregistered [ 846.713768] BUG: unable to handle kernel NULL pointer dereference at 00000000000009f8 [ 846.714790] PGD 0 P4D 0 [ 846.715129] Oops: 0000 [#1] SMP PTI [ 846.715472] CPU: 19 PID: 5057 Comm: kworker/19:16 Kdump: loaded Tainted: G OE ——— - - 4.18.0-147.5.1.el8_1.5es.3.x86_64 #1 [ 846.716082] Hardware name: ESPAN GI-25212/X11DPL-i, BIOS 2.1 06/15/2018 [ 846.716451] Workqueue: events cache_set_flush [bcache] [ 846.716808] RIP: 0010:cache_set_flush+0xc9/0x1b0 [bcache] [ 846.717155] Code: 00 4c 89 a5 b0 03 00 00 48 8b 85 68 f6 ff ff a8 08 0f 84 88 00 00 00 31 db 66 83 bd 3c f7 ff ff 00 48 8b 85 48 ff ff ff 74 28 <48> 8b b8 f8 09 00 0 —truncated—

Weakness

The product dereferences a pointer that it expects to be valid but is NULL.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/1e46ed947ec658f89f1a910d880cd05e42d3763e
• https://git.kernel.org/stable/c/1f25f2d3fa29325320c19a30abf787e0bd5fc91b
• https://git.kernel.org/stable/c/3f9e128186c99a117e304f1dce6d0b9e50c63cd8
• https://git.kernel.org/stable/c/553f560e0a74a7008ad9dba05c3fd05da296befb
• https://git.kernel.org/stable/c/667c3f52373ff5354cb3543e27237eb7df7b2333
• https://git.kernel.org/stable/c/c4f5e7e417034b05f5d2f5fa9a872db897da69bd
• https://git.kernel.org/stable/c/d54681938b777488e5dfb781b566d16adad991de
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html