vfio/platform: check the bounds of read/write syscalls

count and offset are passed from user space and not checked, only
offset is capped to 40 bits, which can be used to read/write out of
bounds of the device.

Fixes: 6e3f264 (“vfio/platform: read and write support for the device fd”)
Cc: [email protected]
Reported-by: Mostafa Saleh <[email protected]>
Reviewed-by: Eric Auger <[email protected]>
Reviewed-by: Mostafa Saleh <[email protected]>
Tested-by: Mostafa Saleh <[email protected]>
Signed-off-by: Alex Williamson <[email protected]>

Author: Alex Williamson

drivers/vfio/platform/vfio_platform_common.c

@@ -388,6 +388,11 @@ static ssize_t vfio_platform_read_mmio(struct vfio_platform_region *reg,
 {
 	unsigned int done = 0;
 
+	if (off >= reg->size)
+		return -EINVAL;
+
+	count = min_t(size_t, count, reg->size - off);
+
 	if (!reg->ioaddr) {
 		reg->ioaddr =
 			ioremap(reg->addr, reg->size);
@@ -467,6 +472,11 @@ static ssize_t vfio_platform_write_mmio(struct vfio_platform_region *reg,
 {
 	unsigned int done = 0;
 
+	if (off >= reg->size)
+		return -EINVAL;
+
+	count = min_t(size_t, count, reg->size - off);
+
 	if (!reg->ioaddr) {
 		reg->ioaddr =
 			ioremap(reg->addr, reg->size);