[PATCH v3 2/3] PCI: Prevent overflow in proc_bus_pci_write()

[Ziming Du <duziming2@huawei.com>]

From: Yongqiang Liu <liuyongqiang13@huawei.com>

When the value of *ppos over the INT_MAX, the pos is over set to a
negative value which will be passed to get_user() or
pci_user_write_config_dword(). Unexpected behavior such as a soft lockup
will happen as follows:

 watchdog: BUG: soft lockup - CPU#0 stuck for 130s! [syz.3.109:3444]
 RIP: 0010:_raw_spin_unlock_irq+0x17/0x30
 Call Trace:
  <TASK>
  pci_user_write_config_dword+0x126/0x1f0
  proc_bus_pci_write+0x273/0x470
  proc_reg_write+0x1b6/0x280
  do_iter_write+0x48e/0x790
  vfs_writev+0x125/0x4a0
  __x64_sys_pwritev+0x1e2/0x2a0
  do_syscall_64+0x59/0x110
  entry_SYSCALL_64_after_hwframe+0x78/0xe2

Fix this by using unsigned int for the pos.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: Ziming Du <duziming2@huawei.com>
---
 drivers/pci/proc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index 9348a0fb8084..2d51b26edbe7 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -113,10 +113,14 @@ 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;
+	int pos;
 	int size = dev->cfg_size;
 	int cnt, ret;
 
+	if (*ppos > INT_MAX)
+		return -EINVAL;
+	pos = *ppos;
+
 	ret = security_locked_down(LOCKDOWN_PCI_ACCESS);
 	if (ret)
 		return ret;
-- 
2.43.0