[PATCH 13/13] android: ram_console: honor dmesg_restrict

[John Stultz <john.stultz@linaro.org>]

From: Nick Kralevich <nnk@google.com>

The Linux kernel has a setting called dmesg_restrict. When true,
only processes with CAP_SYSLOG can view the kernel dmesg logs. This
helps prevent leaking of kernel information into user space.

On Android, it's possible to bypass these restrictions by viewing
/proc/last_kmsg.

This change makes /proc/last_kmsg require the same permissions as
dmesg.

Bug: 5555691
CC: Greg KH <gregkh@linuxfoundation.org>
CC: Android Kernel Team <kernel-team@android.com>
Change-Id: I50ecb74012ef2ac0a3cff7325192634341fddae9
Signed-off-by: Nick Kralevich <nnk@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
 drivers/staging/android/ram_console.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/staging/android/ram_console.c b/drivers/staging/android/ram_console.c
index d956b84..b242be2 100644
--- a/drivers/staging/android/ram_console.c
+++ b/drivers/staging/android/ram_console.c
@@ -99,6 +99,9 @@ static ssize_t ram_console_read_old(struct file *file, char __user *buf,
 	char *str;
 	int ret;
 
+	if (dmesg_restrict && !capable(CAP_SYSLOG))
+		return -EPERM;
+
 	/* Main last_kmsg log */
 	if (pos < old_log_size) {
 		count = min(len, (size_t)(old_log_size - pos));
-- 
1.7.3.2.146.gca209