Re: [PATCH 1/2] firewire: Kill unnecessary buf check in device_attribute.show

["Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>]

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On 18/03/2024 12:46, Takashi Sakamoto wrote:
> Hi,
> 
> On Mon, Jan 22, 2024 at 05:56:04PM +0900, Takashi Sakamoto wrote:
>> Hi,
>>
>> On Mon, Jan 22, 2024 at 01:39:41PM +0800, Li Zhijian wrote:
>>> Per Documentation/filesystems/sysfs.rst:
>>>> sysfs allocates a buffer of size (PAGE_SIZE) and passes it to the
>>>> method.
>>>
>>> So we can kill the unnecessary buf check safely.
>>>
>>> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
>>> ---
>>>   drivers/firewire/core-device.c | 14 +++-----------
>>>   1 file changed, 3 insertions(+), 11 deletions(-)
>>
>> Applied both patches to linux-next branch, since they are not so-urgent
>> fixes.
> 
> I realized that it causes an issue at the path to initialize device
> structure for node in IEEE 1394 bus.
> 
> (drivers/firewire/core-device.c)
> fw_device_init() / fw_device_refresh()
> ->create_units()
>    ->init_fw_attribute_group()
>      ->attr->show(dev, attr, NULL)
> 
> kernel: ------------[ cut here ]------------
> kernel: invalid sysfs_emit: buf:0000000000000000
> kernel: WARNING: CPU: 5 PID: 647501 at fs/sysfs/file.c:747 sysfs_emit+0xb5/0xc0
> kernel: Modules linked in: snd_fireworks(OE) snd_firewire_lib(OE) firewire_ohci(OE) firewire_core(OE) cfg80211 veth nft_masq crc_itu_t vfio_pci vfio_pci_core vfio_iommu_type1 vfio iommufd rpcsec_gss_krb5 nfsv4 nfs netfs snd_seq_dummy sn>
> kernel:  crypto_simd asus_wmi snd_timer ledtrig_audio cryptd cec sparse_keymap nls_iso8859_1 rapl platform_profile wmi_bmof k10temp i2c_piix4 snd rc_core i2c_algo_bit ccp soundcore zfs(PO) spl(O) input_leds joydev cdc_mbim cdc_wdm mac_h>
> kernel: CPU: 5 PID: 647501 Comm: kworker/5:0 Tainted: P        W  OE      6.8.0-11-generic #11-Ubuntu
> kernel: Hardware name: System manufacturer System Product Name/TUF GAMING X570-PLUS, BIOS 5003 10/07/2023
> kernel: Workqueue: firewire fw_device_workfn [firewire_core]
> kernel: RIP: 0010:sysfs_emit+0xb5/0xc0
> kernel: Code: 25 28 00 00 00 75 29 c9 31 d2 31 c9 31 f6 31 ff 45 31 c0 45 31 c9 e9 5a 89 c7 00 48 89 fe 48 c7 c7 64 06 3f bd e8 1b 80 b4 ff <0f> 0b 31 c0 eb c7 e8 a0 ea c5 00 90 90 90 90 90 90 90 90 90 90 90
> kernel: RSP: 0018:ffffacd857103cd0 EFLAGS: 00010246
> kernel: RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> kernel: RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> kernel: RBP: ffffacd857103d20 R08: 0000000000000000 R09: 0000000000000000
> kernel: R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000010000
> kernel: R13: ffffffffc28e2ff8 R14: 0000000000000000 R15: 0000000000000001
> kernel: FS:  0000000000000000(0000) GS:ffff918190080000(0000) knlGS:0000000000000000
> kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> kernel: CR2: 00007835dca0b048 CR3: 00000003cb898000 CR4: 00000000003506f0
> kernel: Call Trace:
> kernel:  <TASK>
> kernel:  ? show_regs+0x6d/0x80
> kernel:  ? __warn+0x89/0x160
> kernel:  ? sysfs_emit+0xb5/0xc0
> kernel:  ? report_bug+0x17e/0x1b0
> kernel:  ? handle_bug+0x51/0xa0
> kernel:  ? exc_invalid_op+0x18/0x80
> kernel:  ? asm_exc_invalid_op+0x1b/0x20
> kernel:  ? sysfs_emit+0xb5/0xc0
> kernel:  show_immediate+0x13f/0x1d0 [firewire_core]
> kernel:  init_fw_attribute_group+0x81/0x150 [firewire_core]
> kernel:  create_units+0x119/0x160 [firewire_core]
> kernel:  fw_device_init+0x1a9/0x330 [firewire_core]
> kernel:  fw_device_workfn+0x12/0x20 [firewire_core]
> kernel:  process_one_work+0x16f/0x350
> kernel:  worker_thread+0x306/0x440
> kernel:  ? __pfx_worker_thread+0x10/0x10
> kernel:  kthread+0xf2/0x120
> kernel:  ? __pfx_kthread+0x10/0x10
> kernel:  ret_from_fork+0x47/0x70
> kernel:  ? __pfx_kthread+0x10/0x10
> kernel:  ret_from_fork_asm+0x1b/0x30
> kernel:  </TASK>
> kernel: ---[ end trace 0000000000000000 ]---
> kernel: ------------[ cut here ]------------
> 
> Furthermore, 'show_text_leaf()' returns negative value when the NULL
> pointer is passed. It results in the lack of vendor/model names from
> sysfs.
> 
> I absolutely overlooked them. I would like to fix them within this merge
> window, or revert them as a last resort...
> 

Sorry for the mistake. I haven't considered callers from other than sysfs.
I'm fine to reverting both *two*.

If we are interesting in the sysfs_emit conversion one, i cooked(see the attachment)
a patch to revert "firewire: Kill unnecessary buf check in device_attribute.show" only.

(Feel free to ignore it if you have had a local fix.)


Thanks
Zhijian




> 
> Regards
> 
> Takashi Sakamoto

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From 96ad3e15b86e2504f3c17fd6a10be48e5ff81cb1 Mon Sep 17 00:00:00 2001
From: Li Zhijian <lizhijian@fujitsu.com>
Date: Mon, 18 Mar 2024 14:05:32 +0800
Subject: [PATCH] Revert "firewire: Kill unnecessary buf check in
 device_attribute.show"

This reverts commit 4a2b06ca33763b363038d333274e212db6ff0de1.

The previous fix didn't consider callers from other than sysfs. Revert
it to fix the NULL dereference

 kernel:  ? sysfs_emit+0xb5/0xc0
 kernel:  show_immediate+0x13f/0x1d0 [firewire_core]
 kernel:  init_fw_attribute_group+0x81/0x150 [firewire_core]
 kernel:  create_units+0x119/0x160 [firewire_core]
 kernel:  fw_device_init+0x1a9/0x330 [firewire_core]
 kernel:  fw_device_workfn+0x12/0x20 [firewire_core]
 kernel:  process_one_work+0x16f/0x350
 kernel:  worker_thread+0x306/0x440
 kernel:  ? __pfx_worker_thread+0x10/0x10
 kernel:  kthread+0xf2/0x120
 kernel:  ? __pfx_kthread+0x10/0x10
 kernel:  ret_from_fork+0x47/0x70
 kernel:  ? __pfx_kthread+0x10/0x10
 kernel:  ret_from_fork_asm+0x1b/0x30
 kernel:  </TASK>
 kernel: ---[ end trace 0000000000000000 ]---
 kernel: ------------[ cut here ]------------

Fixes: 4a2b06ca3376 ("firewire: Kill unnecessary buf check in device_attribute.show")
Reported-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
---
 drivers/firewire/core-device.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
index c0976f6268d3..f208a02d0ebf 100644
--- a/drivers/firewire/core-device.c
+++ b/drivers/firewire/core-device.c
@@ -322,7 +322,7 @@ static ssize_t show_immediate(struct device *dev,
 	if (value < 0)
 		return -ENOENT;
 
-	return sysfs_emit(buf, "0x%06x\n", value);
+	return buf ? sysfs_emit(buf, "0x%06x\n", value) : 0;
 }
 
 #define IMMEDIATE_ATTR(name, key)				\
@@ -334,6 +334,8 @@ static ssize_t show_text_leaf(struct device *dev,
 	struct config_rom_attribute *attr =
 		container_of(dattr, struct config_rom_attribute, attr);
 	const u32 *directories[] = {NULL, NULL};
+	size_t bufsize;
+	char dummy_buf[2];
 	int i, ret = -ENOENT;
 
 	down_read(&fw_device_rwsem);
@@ -355,9 +357,15 @@ static ssize_t show_text_leaf(struct device *dev,
 		}
 	}
 
+	if (buf) {
+		bufsize = PAGE_SIZE - 1;
+	} else {
+		buf = dummy_buf;
+		bufsize = 1;
+	}
+
 	for (i = 0; i < ARRAY_SIZE(directories) && !!directories[i]; ++i) {
-		int result = fw_csr_string(directories[i], attr->key, buf,
-					   PAGE_SIZE - 1);
+		int result = fw_csr_string(directories[i], attr->key, buf, bufsize);
 		// Detected.
 		if (result >= 0) {
 			ret = result;
@@ -366,7 +374,7 @@ static ssize_t show_text_leaf(struct device *dev,
 			// in the root directory follows to the directory entry for vendor ID
 			// instead of the immediate value for vendor ID.
 			result = fw_csr_string(directories[i], CSR_DIRECTORY | attr->key, buf,
-					       PAGE_SIZE - 1);
+					       bufsize);
 			if (result >= 0)
 				ret = result;
 		}
-- 
2.29.2