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Subject[PATCH 04/27] Restrict /dev/mem and /dev/kmem when the kernel is locked down
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From: Matthew Garrett <matthew.garrett@nebula.com>

Allowing users to write to address space makes it possible for the kernel to
be subverted, avoiding module loading restrictions. Prevent this when the
kernel has been locked down.

Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---

drivers/char/mem.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 593a8818aca9..b7c36898b689 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -179,6 +179,9 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
if (p != *ppos)
return -EFBIG;

+ if (kernel_is_locked_down("/dev/mem"))
+ return -EPERM;
+
if (!valid_phys_addr_range(p, count))
return -EFAULT;

@@ -540,6 +543,9 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
int err = 0;

+ if (kernel_is_locked_down("/dev/kmem"))
+ return -EPERM;
+
if (p < (unsigned long) high_memory) {
unsigned long to_write = min_t(unsigned long, count,
(unsigned long)high_memory - p);
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