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Subject[PATCH 04/27] Restrict /dev/{mem,kmem,port} when the kernel is locked down
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From: Matthew Garrett <mjg59@srcf.ucam.org>

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>
Signed-off-by: Matthew Garrett <matthewgarrett@google.com>
---
drivers/char/mem.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b08dc50f9f26..0a2f2e75d5f4 100644
--- 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;
}

--
2.21.0.352.gf09ad66450-goog
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