| Subject | [PATCH 04/27] Restrict /dev/mem and /dev/kmem when the kernel is locked down | From | David Howells <> | Date | Thu, 19 Oct 2017 15:51:02 +0100 |
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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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