patch "drivers: char: mem: Check for address space wraparound with mmap()" added to char-misc-linus

This is a note to let you know that I've just added the patch titled

drivers: char: mem: Check for address space wraparound with mmap()

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Julius Werner <[email protected]>
Date: Fri, 12 May 2017 14:42:58 -0700
Subject: drivers: char: mem: Check for address space wraparound with mmap()

/dev/mem currently allows mmap() mappings that wrap around the end of the physical address space, which should probably be illegal. It circumvents the existing STRICT_DEVMEM permission check because the loop immediately terminates (as the start address is already higher than the end address). On the x86_64 architecture it will then cause a panic (from the BUG(start >= end) in arch/x86/mm/pat.c:reserve_memtype()).

This patch adds an explicit check to make sure offset + size will not wrap around in the physical address type.

---
 drivers/char/mem.c | 5 +++++
 1 file changed, 5 insertions(+)

index 7e4a9d1296bb..6e0cbe092220 100644
@@ -340,6 +340,11 @@ static const struct vm_operations_struct mmap_mem_ops = {
 static int mmap_mem(struct file *file, struct vm_area_struct *vma)
 {
 	size_t size = vma->vm_end - vma->vm_start;
+	phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
+
+	/* It's illegal to wrap around the end of the physical address space. */
+	if (offset + (phys_addr_t)size < offset)
+		return -EINVAL;
 
 	if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
 		return -EINVAL;

2.13.0