Messages in this thread Patch in this message | | | Date | Wed, 29 Mar 2023 19:25:14 +0200 | Subject | Re: BUG FIX: [PATCH v1] memstick_check() memleak in kernel 6.1.0+ introduced pre 4.17 | From | Mirsad Goran Todorovac <> |
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On 23.12.2022. 14:20, Mirsad Goran Todorovac wrote: > Hi all, > > When building a RPM 6.1.0-rc3 for AlmaLinux 8.6, I have enabled CONFIG_DEBUG_KMEMLEAK=y > and the result showed an unreferenced object in kworker process: > > cat /sys/kernel/debug/kmemleak > unreferenced object 0xffff888105028d80 (size 16): > comm "kworker/u12:5", pid 359, jiffies 4294902898 (age 1620.144s) > hex dump (first 16 bytes): > 6d 65 6d 73 74 69 63 6b 30 00 00 00 00 00 00 00 memstick0....... > backtrace: > [<ffffffffb6bb5542>] slab_post_alloc_hook+0xb2/0x340 > [<ffffffffb6bbbf5f>] __kmem_cache_alloc_node+0x1bf/0x2c0 > [<ffffffffb6af8175>] __kmalloc_node_track_caller+0x55/0x160 > [<ffffffffb6ae34a6>] kstrdup+0x36/0x60 > [<ffffffffb6ae3508>] kstrdup_const+0x28/0x30 > [<ffffffffb70d0757>] kvasprintf_const+0x97/0xd0 > [<ffffffffb7c9cdf4>] kobject_set_name_vargs+0x34/0xc0 > [<ffffffffb750289b>] dev_set_name+0x9b/0xd0 > [<ffffffffc12d9201>] memstick_check+0x181/0x639 [memstick] > [<ffffffffb676e1d6>] process_one_work+0x4e6/0x7e0 > [<ffffffffb676e556>] worker_thread+0x76/0x770 > [<ffffffffb677b468>] kthread+0x168/0x1a0 > [<ffffffffb6604c99>] ret_from_fork+0x29/0x50 > > mtodorov@domac:~/linux/kernel/linux_stable$ git bisect log > git bisect start > # bad: [f0c4d9fc9cc9462659728d168387191387e903cc] Linux 6.1-rc4 > git bisect bad f0c4d9fc9cc9462659728d168387191387e903cc > # bad: [fbd56ddcecab5a3623a89c8e941fdbcc55b41045] Linux 6.0.1 > git bisect bad fbd56ddcecab5a3623a89c8e941fdbcc55b41045 > # bad: [7e18e42e4b280c85b76967a9106a13ca61c16179] Linux 6.0-rc4 > git bisect bad 7e18e42e4b280c85b76967a9106a13ca61c16179 > # bad: [568035b01cfb107af8d2e4bd2fb9aea22cf5b868] Linux 6.0-rc1 > git bisect bad 568035b01cfb107af8d2e4bd2fb9aea22cf5b868 > # bad: [84df9525b0c27f3ebc2ebb1864fa62a97fdedb7d] Linux 4.19 > git bisect bad 84df9525b0c27f3ebc2ebb1864fa62a97fdedb7d > # bad: [94710cac0ef4ee177a63b5227664b38c95bbf703] Linux 4.18 > git bisect bad 94710cac0ef4ee177a63b5227664b38c95bbf703 > # bad: [29dcea88779c856c7dc92040a0c01233263101d4] Linux 4.17 > git bisect bad 29dcea88779c856c7dc92040a0c01233263101d4 > > Greg asked me if I would help bisect the bug, since I failed to reproduce it on pre 4.17 kernels, because they wouldn't boot (black > screen) on the Lenovo ALmaLinux 8.7 (CentOS fork) desktop box that only reproduced that bug: > > product: 10TX000VCR (LENOVO_MT_10TX_BU_Lenovo_FM_V530S-07ICB) > vendor: LENOVO > version: V530S-07ICB > > I would welcome any advice. > > Please find attached the lshw output and the build config from the last kernel version that also exhibits this bug, so the > conclusion is that it is not fixed since the report on November 29th 2022: > > https://lore.kernel.org/regressions/0d9c3f6c-3948-d5d1-bcc1-baf31141beaa@alu.unizg.hr/T/#t > > With the hint of Tvrtko, I was able to extract the correct list of maintainers this time. > > The bug occurs in one kernel memory leak, and it is unobvious whether a skilled attacker could use an abusive program to trigger the > leak of enough 16 byte slabs (and overhead) to exhaust kernel memory and cause denial-of-service (crash of the system). > > I apologise for the first unsuccessful attempt.
static struct memstick_dev *memstick_alloc_card(struct memstick_host *host)
calls dev_set_name(&card->dev, "%s", dev_name(&host->dev)); that calls err = kobject_set_name_vargs(&dev->kobj, fmt, vargs); that executes:
if (strchr(s, '/')) { char *t;
t = kstrdup(s, GFP_KERNEL); kfree_const(s); if (!t) return -ENOMEM; strreplace(t, '/', '!'); s = t; } kfree_const(kobj->name); kobj->name = s;
so, this kobj->name was never freed in the "goto err_out" case in line 404.
380 static struct memstick_dev *memstick_alloc_card(struct memstick_host *host) 381 { 382 struct memstick_dev *card = kzalloc(sizeof(struct memstick_dev), 383 GFP_KERNEL); 384 struct memstick_dev *old_card = host->card; 385 struct ms_id_register id_reg; 386 387 if (card) { 388 card->host = host; 389 dev_set_name(&card->dev, "%s", dev_name(&host->dev)); 390 card->dev.parent = &host->dev; 391 card->dev.bus = &memstick_bus_type; 392 card->dev.release = memstick_free_card; 393 card->check = memstick_dummy_check; 394 395 card->reg_addr.r_offset = offsetof(struct ms_register, id); 396 card->reg_addr.r_length = sizeof(id_reg); 397 card->reg_addr.w_offset = offsetof(struct ms_register, id); 398 card->reg_addr.w_length = sizeof(id_reg); 399 400 init_completion(&card->mrq_complete); 401 402 host->card = card; 403 if (memstick_set_rw_addr(card)) 404 goto err_out; 405 406 card->next_request = h_memstick_read_dev_id; 407 memstick_new_req(host); 408 wait_for_completion(&card->mrq_complete); 409 410 if (card->current_mrq.error) 411 goto err_out; 412 } 413 host->card = old_card; 414 return card; 415 err_out: 416 host->card = old_card; 421 kfree(card); 422 return NULL; 423 }
This little patch fixes it, also at the release() method.
However, release() had not yet been tested, and I am not certain that in that case kobj->name would not be kfree_const()-ed automatically.
Maybe it ought to be separated in two independent patches?
diff --git a/drivers/memstick/core/memstick.c b/drivers/memstick/core/memstick.c index bf7667845459..403ab06e3ffa 100644 --- a/drivers/memstick/core/memstick.c +++ b/drivers/memstick/core/memstick.c @@ -191,6 +191,10 @@ static void memstick_free_card(struct device *dev) { struct memstick_dev *card = container_of(dev, struct memstick_dev, dev); + if ((card->dev).kobj.name) { + kfree_const((card->dev).kobj.name); + (card->dev).kobj.name = NULL; + } kfree(card); }
@@ -410,6 +414,10 @@ static struct memstick_dev *memstick_alloc_card(struct memstick_host *host) return card; err_out: host->card = old_card; + if ((card->dev).kobj.name) { + kfree_const((card->dev).kobj.name); + (card->dev).kobj.name = NULL; + } kfree(card); return NULL; } This morning I did not feel like we'd fix two memory leaks today.
This one was a nag for three months :-)
Of course, this requires peer review. The fact that it fixed the /sys/kernel/debug/kmemleak output doesn't mean that it wouldn't break something, does it?
It is clearly the good wind of the Providence.
Best regards, Mirsad
-- Mirsad Todorovac System engineer Faculty of Graphic Arts | Academy of Fine Arts University of Zagreb Republic of Croatia, the European Union Sistem inženjer Grafički fakultet | Akademija likovnih umjetnosti Sveučilište u Zagrebu
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