Messages in this thread Patch in this message | | | From | "Lee, Chun-Yi" <> | Subject | [PATCH 2/2] PM / Sleep: Check the file capability when writing wake lock interface | Date | Sun, 30 Dec 2018 21:28:56 +0800 |
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The wake lock/unlock sysfs interfaces check that the writer must has CAP_BLOCK_SUSPEND capability. But the checking logic can be bypassed by opening sysfs file within an unprivileged process and then writing the file within a privileged process. The tricking way has been exposed by Andy Lutomirski in CVE-2013-1959.
Here is an example that it's a simplified version from CVE-2013-1959 to bypass the capability checking of wake_lock sysfs:
int main(int argc, char* argv[]) { int fd, ret = 0;
fd = open("/sys/power/wake_lock", O_RDWR); if (fd < 0) err(1, "open wake_lock");
if (dup2(fd, 1) != 1) err(1, "dup2"); sleep(1); execl("./string", "string");
return ret; }
The string is a privileged program that it can be used to write string to wake_lock interface. The main unprivileged process opens the sysfs interface and overwrites stdout. So the privileged process will write to wake_lock.
This patch implemented the callback of file capable checking hook in kobject attribute level. It will check the opener's capability.
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> Cc: Chen Yu <yu.c.chen@intel.com> Cc: Giovanni Gherdovich <ggherdovich@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Pavel Machek <pavel@ucw.cz> Cc: Len Brown <len.brown@intel.com> Cc: "Martin K. Petersen" <martin.petersen@oracle.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Joe Perches <joe@perches.com> Cc: Bart Van Assche <bvanassche@acm.org> Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com> --- kernel/power/main.c | 14 ++++++++++++++ kernel/power/wakelock.c | 6 ------ 2 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/kernel/power/main.c b/kernel/power/main.c index 98e76cad128b..265199efedc1 100644 --- a/kernel/power/main.c +++ b/kernel/power/main.c @@ -661,6 +661,11 @@ static ssize_t wake_lock_store(struct kobject *kobj, return error ? error : n; } +static bool wake_lock_store_file_capable(const struct file *file) +{ + return file_ns_capable(file, &init_user_ns, CAP_BLOCK_SUSPEND); +} + power_attr(wake_lock); static ssize_t wake_unlock_show(struct kobject *kobj, @@ -678,6 +683,11 @@ static ssize_t wake_unlock_store(struct kobject *kobj, return error ? error : n; } +static bool wake_unlock_store_file_capable(const struct file *file) +{ + return file_ns_capable(file, &init_user_ns, CAP_BLOCK_SUSPEND); +} + power_attr(wake_unlock); #endif /* CONFIG_PM_WAKELOCKS */ @@ -803,6 +813,10 @@ static int __init pm_init(void) power_kobj = kobject_create_and_add("power", NULL); if (!power_kobj) return -ENOMEM; +#ifdef CONFIG_PM_WAKELOCKS + wake_lock_attr.store_file_capable = wake_lock_store_file_capable; + wake_unlock_attr.store_file_capable = wake_unlock_store_file_capable; +#endif error = sysfs_create_group(power_kobj, &attr_group); if (error) return error; diff --git a/kernel/power/wakelock.c b/kernel/power/wakelock.c index 4210152e56f0..52a4cfe55eb5 100644 --- a/kernel/power/wakelock.c +++ b/kernel/power/wakelock.c @@ -205,9 +205,6 @@ int pm_wake_lock(const char *buf) size_t len; int ret = 0; - if (!capable(CAP_BLOCK_SUSPEND)) - return -EPERM; - while (*str && !isspace(*str)) str++; @@ -251,9 +248,6 @@ int pm_wake_unlock(const char *buf) size_t len; int ret = 0; - if (!capable(CAP_BLOCK_SUSPEND)) - return -EPERM; - len = strlen(buf); if (!len) return -EINVAL; -- 2.13.6
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