Restrict /dev/{mem,kmem,port} when the kernel is locked down

Allowing users to read and write to core kernel memory makes it possible
for the kernel to be subverted, avoiding module loading restrictions, and
also to steal cryptographic information.

Disallow /dev/mem and /dev/kmem from being opened this when the kernel has
been locked down to prevent this.

Also disallow /dev/port from being opened to prevent raw ioport access and
thus DMA from being used to accomplish the same thing.

Signed-off-by: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0005-Restrict-dev-mem-kmem-port-when-the-kernel-is-locked.patch

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b08dc50f9f26026730c5eb12ee8e4be47012c2f8..0a2f2e75d5f450a1a74190b3452b2c38549c9bc2 100644 (file)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -786,6 +786,8 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
 
 static int open_port(struct inode *inode, struct file *filp)
 {
+       if (kernel_is_locked_down("/dev/mem,kmem,port"))
+               return -EPERM;
        return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
 }