[PATCH v2 2/3] PCI: Prevent overflow in proc_bus_pci_write()

[Ziming Du]

From: Yongqiang Liu <liuyongqiang13@xxxxxxxxxx>

When the value of ppos over the INT_MAX, the pos is over set to a negtive
value which will be passed to get_user() or pci_user_write_config_dword().
Unexpected behavior such as a softlock 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 add check for the pos.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Yongqiang Liu <liuyongqiang13@xxxxxxxxxx>
Signed-off-by: Ziming Du <duziming2@xxxxxxxxxx>
---
 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..200d42feafd8 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -121,7 +121,7 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 	if (ret)
 		return ret;
 
-	if (pos >= size)
+	if (pos >= size || pos < 0)
 		return 0;
 	if (nbytes >= size)
 		nbytes = size;
-- 
2.43.0