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

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Tue, 16 Dec 2025, Ziming Du wrote:

> When the value of ppos over the INT_MAX, the pos will be

is over

> set a negtive value which will be pass to get_user() or

set to a negative value which will be passed

> pci_user_write_config_dword(). And unexpected behavior

Please start the sentence with something else than And.

Hmm, the lines look rather short too, can you please reflow the changelog 
paragraphs to 75 characters.

> 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

Could you please trim the dump so it only contains things relevant to this 
issue () (also check trimming in the other patches).

> Fix this by use 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 | 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;

So this still throws away some bits compared with the original ppos ?

-- 
 i.