From 3caf7a8709535c629af06fdc2981ce990a749a8b Mon Sep 17 00:00:00 2001 From: Henrique de Moraes Holschuh Date: Mon, 24 Jan 2011 08:11:01 -0700 Subject: [PATCH] thinkpad-acpi: lock down video output state access Back ported from commit b525c06cdbd8a3963f0173ccd23f9147d4c384b5 upstream by Tim Gardner . Resolves CVE-2010-3448 Given the right combination of ThinkPad and X.org, just reading the video output control state is enough to hard-crash X.org. Until the day I somehow find out a model or BIOS cut date to not provide this feature to ThinkPads that can do video switching through X RandR, change permissions so that only processes with CAP_SYS_ADMIN can access any sort of video output control state. This bug could be considered a local DoS I suppose, as it allows any non-privledged local user to cause some versions of X.org to hard-crash some ThinkPads. Reported-by: Jidanni Signed-off-by: Henrique de Moraes Holschuh Signed-off-by: Greg Kroah-Hartman Signed-off-by: Tim Gardner --- Documentation/laptops/thinkpad-acpi.txt | 4 ++++ drivers/platform/x86/Kconfig | 10 ++++++++-- drivers/platform/x86/thinkpad_acpi.c | 18 +++++++++++++++--- 3 files changed, 27 insertions(+), 5 deletions(-) diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt index e2ddcde..fa12ef8 100644 --- a/Documentation/laptops/thinkpad-acpi.txt +++ b/Documentation/laptops/thinkpad-acpi.txt @@ -674,6 +674,10 @@ LCD, CRT or DVI (if available). The following commands are available: echo expand_toggle > /proc/acpi/ibm/video echo video_switch > /proc/acpi/ibm/video +NOTE: Access to this feature is restricted to processes owning the +CAP_SYS_ADMIN capability for safety reasons, as it can interact badly +enough with some versions of X.org to crash it. + Each video output device can be enabled or disabled individually. Reading /proc/acpi/ibm/video shows the status of each device. diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig index 77c6097..bbe9036 100644 --- a/drivers/platform/x86/Kconfig +++ b/drivers/platform/x86/Kconfig @@ -290,9 +290,15 @@ config THINKPAD_ACPI_VIDEO server running, phase of the moon, and the current mood of Schroedinger's cat. If you can use X.org's RandR to control your ThinkPad's video output ports instead of this feature, - don't think twice: do it and say N here to save some memory. + don't think twice: do it and say N here to save memory and avoid + bad interactions with X.org. - If you are not sure, say Y here. + NOTE: access to this feature is limited to processes with the + CAP_SYS_ADMIN capability, to avoid local DoS issues in platforms + where it interacts badly with X.org. + + If you are not sure, say Y here but do try to check if you could + be using X.org RandR instead. config THINKPAD_ACPI_HOTKEY_POLL bool "Support NVRAM polling for hot keys" diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c index 05e5d56..a83803f 100644 --- a/drivers/platform/x86/thinkpad_acpi.c +++ b/drivers/platform/x86/thinkpad_acpi.c @@ -235,6 +235,7 @@ struct ibm_init_struct { char param[32]; int (*init) (struct ibm_init_struct *); + mode_t base_procfs_mode; struct ibm_struct *data; }; @@ -4142,6 +4143,10 @@ static int video_read(char *p) return len; } + /* Even reads can crash X.org, so... */ + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + status = video_outputsw_get(); if (status < 0) return status; @@ -4175,6 +4180,10 @@ static int video_write(char *buf) if (video_supported == TPACPI_VIDEO_NONE) return -ENODEV; + /* Even reads can crash X.org, let alone writes... */ + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + enable = 0; disable = 0; @@ -7357,9 +7366,11 @@ static int __init ibm_init(struct ibm_init_struct *iibm) "%s installed\n", ibm->name); if (ibm->read) { - entry = create_proc_entry(ibm->name, - S_IFREG | S_IRUGO | S_IWUSR, - proc_dir); + mode_t mode = iibm->base_procfs_mode; + + if (!mode) + mode = S_IRUGO; + entry = create_proc_entry(ibm->name, mode, proc_dir); if (!entry) { printk(TPACPI_ERR "unable to create proc entry %s\n", ibm->name); @@ -7555,6 +7566,7 @@ static struct ibm_init_struct ibms_init[] __initdata = { #ifdef CONFIG_THINKPAD_ACPI_VIDEO { .init = video_init, + .base_procfs_mode = S_IRUSR, .data = &video_driver_data, }, #endif -- 1.7.0.4