From f3ce5ab4904628fbe9d659b43db4bb6b609bb887 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Pali=20Roh=C3=A1r?= Date: Sat, 18 Jun 2016 00:54:45 +0200 Subject: hwmon: (dell-smm) Restrict fan control and serial number to CAP_SYS_ADMIN by default MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit commit 7613663cc186f8f3c50279390ddc60286758001c upstream. 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 Signed-off-by: Pali Rohár Signed-off-by: Guenter Roeck [bwh: Backported to 3.16: adjust filename, context] Signed-off-by: Ben Hutchings --- drivers/char/i8k.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) (limited to 'drivers') diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c index 93dcad0c1cbe..89d1284e67f0 100644 --- a/drivers/char/i8k.c +++ b/drivers/char/i8k.c @@ -62,6 +62,7 @@ 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 int i8k_fan_mult; @@ -85,13 +86,13 @@ static bool ignore_dmi; module_param(ignore_dmi, bool, 0); MODULE_PARM_DESC(ignore_dmi, "Continue probing hardware even if DMI data does not match"); -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)"); static int fan_mult = I8K_FAN_MULT; module_param(fan_mult, int, 0); @@ -350,9 +351,11 @@ 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: @@ -469,7 +472,7 @@ static int i8k_proc_show(struct seq_file *seq, void *offset) return 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); @@ -765,6 +768,8 @@ 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 -- cgit v1.2.3