linux-kernel - [PATCH 3/3] PCI: Prevent overflow in proc_bus_pci

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Message-ID: <20251216083912.758219-4-duziming2@huawei.com>
Date: Tue, 16 Dec 2025 16:39:12 +0800
From: Ziming Du <duziming2@...wei.com>
To: <bhelgaas@...gle.com>
CC: <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<chrisw@...hat.com>, <jbarnes@...tuousgeek.org>,
	<alex.williamson@...hat.com>, <liuyongqiang13@...wei.com>,
	<duziming2@...wei.com>
Subject: [PATCH 3/3] PCI: Prevent overflow in proc_bus_pci_write()

When the value of ppos over the INT_MAX, the pos will be
set a negtive value which will be pass to get_user() or
pci_user_write_config_dword(). And unexpected behavior
such as a softlock happens:

 watchdog: BUG: soft lockup - CPU#0 stuck for 130s! [syz.3.109:3444]
 Modules linked in:
 CPU: 0 PID: 3444 Comm: syz.3.109 Not tainted 6.6.0+ #33
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
 RIP: 0010:_raw_spin_unlock_irq+0x17/0x30
 Code: cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 e8 52 12 00 00 90 fb 65 ff 0d b1 a1 86 6d <74> 05 e9 42 52 00 00 0f 1f 44 00 00 c3 cc cc cc cc 0f 1f 84 00 00
 RSP: 0018:ffff88816851fb50 EFLAGS: 00000246
 RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff927daf9b
 RDX: 0000000000000cfc RSI: 0000000000000046 RDI: ffffffff9a7c7400
 RBP: 00000000818bb9dc R08: 0000000000000001 R09: ffffed102d0a3f59
 R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000000000
 R13: ffff888102220000 R14: ffffffff926d3b10 R15: 00000000210bbb5f
 FS:  00007ff2d4e56640(0000) GS:ffff8881f5c00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00000000210bbb5b CR3: 0000000147374002 CR4: 0000000000772ef0
 PKRU: 00000000
 Call Trace:
  <TASK>
  pci_user_write_config_dword+0x126/0x1f0
  ? __get_user_nocheck_8+0x20/0x20
  proc_bus_pci_write+0x273/0x470
  proc_reg_write+0x1b6/0x280
  do_iter_write+0x48e/0x790
  ? import_iovec+0x47/0x90
  vfs_writev+0x125/0x4a0
  ? futex_wake+0xed/0x500
  ? __pfx_vfs_writev+0x10/0x10
  ? userfaultfd_ioctl+0x131/0x1ae0
  ? userfaultfd_ioctl+0x131/0x1ae0
  ? do_futex+0x17e/0x220
  ? __pfx_do_futex+0x10/0x10
  ? __fget_files+0x193/0x2b0
  __x64_sys_pwritev+0x1e2/0x2a0
  ? __pfx___x64_sys_pwritev+0x10/0x10
  do_syscall_64+0x59/0x110
  entry_SYSCALL_64_after_hwframe+0x78/0xe2

Fix this by use unsigned int for the pos.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Yongqiang Liu <liuyongqiang13@...wei.com>
Signed-off-by: Ziming Du <duziming2@...wei.com>
---
 drivers/pci/proc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index 9348a0fb8084..dbec1d4209c9 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -113,7 +113,7 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 {
 	struct inode *ino = file_inode(file);
 	struct pci_dev *dev = pde_data(ino);
-	int pos = *ppos;
+	unsigned int pos = *ppos;
 	int size = dev->cfg_size;
 	int cnt, ret;
 
-- 
2.43.0