x86: introduce /dev/mem restrictions with a config option
This patch introduces a restriction on /dev/mem: Only non-memory can be
read or written unless the newly introduced config option is set.
The X server needs access to /dev/mem for the PCI space, but it doesn't need
access to memory; both the file permissions and SELinux permissions of /dev/mem
just make X effectively super-super powerful. With the exception of the
BIOS area, there's just no valid app that uses /dev/mem on actual memory.
Other popular users of /dev/mem are rootkits and the like.
(note: mmap access of memory via /dev/mem was already not allowed since
a really long time)
People who want to use /dev/mem for kernel debugging can enable the config
option.
The restrictions of this patch have been in the Fedora and RHEL kernels for
at least 4 years without any problems.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 20070b7..dcf6e31 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -108,6 +108,30 @@
}
#endif
+#ifdef CONFIG_NONPROMISC_DEVMEM
+static inline int range_is_allowed(unsigned long from, unsigned long to)
+{
+ unsigned long cursor;
+
+ cursor = from >> PAGE_SHIFT;
+ while ((cursor << PAGE_SHIFT) < to) {
+ if (!devmem_is_allowed(cursor)) {
+ printk(KERN_INFO "Program %s tried to read /dev/mem "
+ "between %lx->%lx.\n",
+ current->comm, from, to);
+ return 0;
+ }
+ cursor++;
+ }
+ return 1;
+}
+#else
+static inline int range_is_allowed(unsigned long from, unsigned long to)
+{
+ return 1;
+}
+#endif
+
/*
* This funcion reads the *physical* memory. The f_pos points directly to the
* memory location.
@@ -157,6 +181,8 @@
*/
ptr = xlate_dev_mem_ptr(p);
+ if (!range_is_allowed(p, p+count))
+ return -EPERM;
if (copy_to_user(buf, ptr, sz))
return -EFAULT;
buf += sz;
@@ -214,6 +240,8 @@
*/
ptr = xlate_dev_mem_ptr(p);
+ if (!range_is_allowed(p, p+sz))
+ return -EPERM;
copied = copy_from_user(ptr, buf, sz);
if (copied) {
written += sz - copied;