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

On Thu, 8 Jan 2026, Ziming Du wrote:

> 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;
> 

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

With the note that proc_bus_pci_read() and proc_bus_pci_write() diverge in 
handling > INT_MAX values and that feels unjustified (but there's not this
same problem on the read side I guess so if the read side is made the same 
as the write side, it would be better to do that in another patch).

-- 
 i.