Re: [PATCH] PCI: fix using __initdata memory after free in disable_acs_redir parameter

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Jan 15, 2019 at 10:32:03AM -0700, Logan Gunthorpe wrote:
> The disable_acs_redir parameter stores a pointer to the string passed to
> pci_setup(). However, the string passed to PCI setup is actually a
> temporary copy allocated in static __initdata memory. After init, once
> the memory is freed, it is no longer valid to reference this pointer.
> 
> This bug was noticed in v5.0-rc1 after a change in commit c5eb1190074c
> ("PCI / PM: Allow runtime PM without callback functions") caused
> pci_disable_acs_redir() to be called during shutdown which manifested
> as an unable to handle kernel paging request at:
> 
> RIP: 0010:pci_enable_acs+0x3f/0x1e0
> Call Trace:
>    pci_restore_state.part.44+0x159/0x3c0
>    pci_restore_standard_config+0x33/0x40
>    pci_pm_runtime_resume+0x2b/0xd0
>    ? pci_restore_standard_config+0x40/0x40
>    __rpm_callback+0xbc/0x1b0
>    rpm_callback+0x1f/0x70
>    ? pci_restore_standard_config+0x40/0x40
>     rpm_resume+0x4f9/0x710
>    ? pci_conf1_read+0xb6/0xf0
>    ? pci_conf1_write+0xb2/0xe0
>    __pm_runtime_resume+0x47/0x70
>    pci_device_shutdown+0x1e/0x60
>    device_shutdown+0x14a/0x1f0
>    kernel_restart+0xe/0x50
>    __do_sys_reboot+0x1ee/0x210
>    ? __fput+0x144/0x1d0
>    do_writev+0x5e/0xf0
>    ? do_writev+0x5e/0xf0
>    do_syscall_64+0x48/0xf0
>    entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> It was also likely possible to trigger this bug when hotplugging PCI
> devices.
> 
> To fix this, instead of storing a pointer, we use kstrdup to copy the
> disable_acs_redir_param to its own buffer which will never be freed.
> 
> Fixes: aaca43fda742 ("PCI: Add "pci=disable_acs_redir=" parameter for peer-to-peer support")
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> Cc: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>

Applied with Jarkko's tested- and reviewed-by to for-linus for v5.0,
thanks!

> ---
>  drivers/pci/pci.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index c9d8e3c837de..c25acace7d91 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6195,7 +6195,8 @@ static int __init pci_setup(char *str)
>  			} else if (!strncmp(str, "pcie_scan_all", 13)) {
>  				pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
>  			} else if (!strncmp(str, "disable_acs_redir=", 18)) {
> -				disable_acs_redir_param = str + 18;
> +				disable_acs_redir_param =
> +					kstrdup(str + 18, GFP_KERNEL);
>  			} else {
>  				printk(KERN_ERR "PCI: Unknown option `%s'\n",
>  						str);
> -- 
> 2.19.0
>