[6/6] thinkpad-acpi: lock down video output state access

Commit Message

Henrique de Moraes Holschuh Feb. 26, 2010, 4:11 a.m. UTC

None

Patch

diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index 75afa12..39c0a09 100644
--- a/Documentation/laptops/thinkpad-acpi.txt
+++ b/Documentation/laptops/thinkpad-acpi.txt
@@ -650,6 +650,10 @@  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 f526e73..11fce79 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -319,9 +319,15 @@  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 3af4628..5d02cc0 100644
--- a/drivers/platform/x86/thinkpad_acpi.c
+++ b/drivers/platform/x86/thinkpad_acpi.c
@@ -286,6 +286,7 @@  struct ibm_init_struct {
 	char param[32];
 
 	int (*init) (struct ibm_init_struct *);
+	mode_t base_procfs_mode;
 	struct ibm_struct *data;
 };
 
@@ -4629,6 +4630,10 @@  static int video_read(struct seq_file *m)
 		return 0;
 	}
 
+	/* Even reads can crash X.org, so... */
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
 	status = video_outputsw_get();
 	if (status < 0)
 		return status;
@@ -4662,6 +4667,10 @@  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;
 
@@ -8487,9 +8496,10 @@  static int __init ibm_init(struct ibm_init_struct *iibm)
 		"%s installed\n", ibm->name);
 
 	if (ibm->read) {
-		mode_t mode;
+		mode_t mode = iibm->base_procfs_mode;
 
-		mode = S_IRUGO;
+		if (!mode)
+			mode = S_IRUGO;
 		if (ibm->write)
 			mode |= S_IWUSR;
 		entry = proc_create_data(ibm->name, mode, proc_dir,
@@ -8680,6 +8690,7 @@  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