linux-kernel - [PATCH] PCI: fix using __initdata memory after free in disable_acs

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Date:   Tue, 15 Jan 2019 10:32:03 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Stephen Bates <sbates@...thlin.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Subject: [PATCH] PCI: fix using __initdata memory after free in disable_acs_redir parameter

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the memory is freed, it is no longer valid to reference this pointer.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@...tatee.com>
Cc: Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
---
 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