| Message ID | 1466204089-17030-3-git-send-email-pali.rohar@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On 06/17/2016 03:54 PM, Pali Rohár wrote: > For security reasons ordinary user must not be able to control fan speed > via /proc/i8k by default. Some malicious software running under "nobody" > user could be able to turn fan off and cause HW problems. So this patch > changes default value of "restricted" parameter to 1. > > Also restrict reading of DMI_PRODUCT_SERIAL from /proc/i8k via "restricted" > parameter. It is because non root user cannot read DMI_PRODUCT_SERIAL from > sysfs file /sys/class/dmi/id/product_serial. > > Old non secure behaviour of file /proc/i8k can be achieved by loading this > module with "restricted" parameter set to 0. > > Note that this patch has effects only for kernels compiled with CONFIG_I8K > and only for file /proc/i8k. Hwmon interface provided by this driver was > not changed and root access for setting fan speed was needed also before. > > Reported-by: Mario Limonciello <Mario_Limonciello@dell.com> > Signed-off-by: Pali Rohár <pali.rohar@gmail.com> > Cc: stable@vger.kernel.org # will need backport Applied. Guenter > --- > drivers/hwmon/dell-smm-hwmon.c | 19 ++++++++++++------- > 1 file changed, 12 insertions(+), 7 deletions(-) > > diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c > index 480b2fa..c8bd3fdd 100644 > --- a/drivers/hwmon/dell-smm-hwmon.c > +++ b/drivers/hwmon/dell-smm-hwmon.c > @@ -67,6 +67,7 @@ > > static DEFINE_MUTEX(i8k_mutex); > static char bios_version[4]; > +static char bios_machineid[16]; > static struct device *i8k_hwmon_dev; > static u32 i8k_hwmon_flags; > static uint i8k_fan_mult = I8K_FAN_MULT; > @@ -95,13 +96,13 @@ module_param(ignore_dmi, bool, 0); > MODULE_PARM_DESC(ignore_dmi, "Continue probing hardware even if DMI data does not match"); > > #if IS_ENABLED(CONFIG_I8K) > -static bool restricted; > +static bool restricted = true; > module_param(restricted, bool, 0); > -MODULE_PARM_DESC(restricted, "Allow fan control if SYS_ADMIN capability set"); > +MODULE_PARM_DESC(restricted, "Restrict fan control and serial number to CAP_SYS_ADMIN (default: 1)"); > > static bool power_status; > module_param(power_status, bool, 0600); > -MODULE_PARM_DESC(power_status, "Report power status in /proc/i8k"); > +MODULE_PARM_DESC(power_status, "Report power status in /proc/i8k (default: 0)"); > #endif > > static uint fan_mult; > @@ -397,9 +398,11 @@ i8k_ioctl_unlocked(struct file *fp, unsigned int cmd, unsigned long arg) > break; > > case I8K_MACHINE_ID: > - memset(buff, 0, 16); > - strlcpy(buff, i8k_get_dmi_data(DMI_PRODUCT_SERIAL), > - sizeof(buff)); > + if (restricted && !capable(CAP_SYS_ADMIN)) > + return -EPERM; > + > + memset(buff, 0, sizeof(buff)); > + strlcpy(buff, bios_machineid, sizeof(buff)); > break; > > case I8K_FN_STATUS: > @@ -516,7 +519,7 @@ static int i8k_proc_show(struct seq_file *seq, void *offset) > seq_printf(seq, "%s %s %s %d %d %d %d %d %d %d\n", > I8K_PROC_FMT, > bios_version, > - i8k_get_dmi_data(DMI_PRODUCT_SERIAL), > + (restricted && !capable(CAP_SYS_ADMIN)) ? "-1" : bios_machineid, > cpu_temp, > left_fan, right_fan, left_speed, right_speed, > ac_power, fn_key); > @@ -985,6 +988,8 @@ static int __init i8k_probe(void) > > strlcpy(bios_version, i8k_get_dmi_data(DMI_BIOS_VERSION), > sizeof(bios_version)); > + strlcpy(bios_machineid, i8k_get_dmi_data(DMI_PRODUCT_SERIAL), > + sizeof(bios_machineid)); > > /* > * Get SMM Dell signature > -- To unsubscribe from this list: send the line "unsubscribe linux-hwmon" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c index 480b2fa..c8bd3fdd 100644 --- a/drivers/hwmon/dell-smm-hwmon.c +++ b/drivers/hwmon/dell-smm-hwmon.c @@ -67,6 +67,7 @@ static DEFINE_MUTEX(i8k_mutex); static char bios_version[4]; +static char bios_machineid[16]; static struct device *i8k_hwmon_dev; static u32 i8k_hwmon_flags; static uint i8k_fan_mult = I8K_FAN_MULT; @@ -95,13 +96,13 @@ module_param(ignore_dmi, bool, 0); MODULE_PARM_DESC(ignore_dmi, "Continue probing hardware even if DMI data does not match"); #if IS_ENABLED(CONFIG_I8K) -static bool restricted; +static bool restricted = true; module_param(restricted, bool, 0); -MODULE_PARM_DESC(restricted, "Allow fan control if SYS_ADMIN capability set"); +MODULE_PARM_DESC(restricted, "Restrict fan control and serial number to CAP_SYS_ADMIN (default: 1)"); static bool power_status; module_param(power_status, bool, 0600); -MODULE_PARM_DESC(power_status, "Report power status in /proc/i8k"); +MODULE_PARM_DESC(power_status, "Report power status in /proc/i8k (default: 0)"); #endif static uint fan_mult; @@ -397,9 +398,11 @@ i8k_ioctl_unlocked(struct file *fp, unsigned int cmd, unsigned long arg) break; case I8K_MACHINE_ID: - memset(buff, 0, 16); - strlcpy(buff, i8k_get_dmi_data(DMI_PRODUCT_SERIAL), - sizeof(buff)); + if (restricted && !capable(CAP_SYS_ADMIN)) + return -EPERM; + + memset(buff, 0, sizeof(buff)); + strlcpy(buff, bios_machineid, sizeof(buff)); break; case I8K_FN_STATUS: @@ -516,7 +519,7 @@ static int i8k_proc_show(struct seq_file *seq, void *offset) seq_printf(seq, "%s %s %s %d %d %d %d %d %d %d\n", I8K_PROC_FMT, bios_version, - i8k_get_dmi_data(DMI_PRODUCT_SERIAL), + (restricted && !capable(CAP_SYS_ADMIN)) ? "-1" : bios_machineid, cpu_temp, left_fan, right_fan, left_speed, right_speed, ac_power, fn_key); @@ -985,6 +988,8 @@ static int __init i8k_probe(void) strlcpy(bios_version, i8k_get_dmi_data(DMI_BIOS_VERSION), sizeof(bios_version)); + strlcpy(bios_machineid, i8k_get_dmi_data(DMI_PRODUCT_SERIAL), + sizeof(bios_machineid)); /* * Get SMM Dell signature
For security reasons ordinary user must not be able to control fan speed via /proc/i8k by default. Some malicious software running under "nobody" user could be able to turn fan off and cause HW problems. So this patch changes default value of "restricted" parameter to 1. Also restrict reading of DMI_PRODUCT_SERIAL from /proc/i8k via "restricted" parameter. It is because non root user cannot read DMI_PRODUCT_SERIAL from sysfs file /sys/class/dmi/id/product_serial. Old non secure behaviour of file /proc/i8k can be achieved by loading this module with "restricted" parameter set to 0. Note that this patch has effects only for kernels compiled with CONFIG_I8K and only for file /proc/i8k. Hwmon interface provided by this driver was not changed and root access for setting fan speed was needed also before. Reported-by: Mario Limonciello <Mario_Limonciello@dell.com> Signed-off-by: Pali Rohár <pali.rohar@gmail.com> Cc: stable@vger.kernel.org # will need backport --- drivers/hwmon/dell-smm-hwmon.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)