This patch fixes a possible kernel crash through stack trashing triggered
by an integer overflow. If count passed from userspace is (size_t)-1lu, the
range check will overflow and return false. So the copy_from_user() will
end up attempting to copy 0xFFFFFFFF (or 0xFFFFFFFFFFFFFFFF) bytes to the kernel stack.
Of course the copy will fail at some point, because we can't allocate a buffer that big.
But it will copy as much as it can and then return with an -EFAULT.
This means the userspace process writing to this proc file controls
the kernel stack.
This is probably not useable for a privilege escalation, because the proc file
has permissions (S_IFREG | S_IRUGO | S_IWUSR). So only root will be able to crash the machine.
Signed-off-by: Michael Buesch <mb@xxxxxxxxx>
Cc: stable@xxxxxxxxxx
---
This patch is completely untested, because I do not have a machine with acpi-video.
---
drivers/acpi/video.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- linux-2.6.orig/drivers/acpi/video.c
+++ linux-2.6/drivers/acpi/video.c
@@ -1185,21 +1185,21 @@ acpi_video_device_write_state(struct fil
const char __user * buffer,
size_t count, loff_t * data)
{
int status;
struct seq_file *m = file->private_data;
struct acpi_video_device *dev = m->private;
char str[12] = { 0 };
u32 state = 0;
- if (!dev || count + 1 > sizeof str)
+ if (!dev || count >= sizeof str)
return -EINVAL;
if (copy_from_user(str, buffer, count))
return -EFAULT;
str[count] = 0;
state = simple_strtoul(str, NULL, 0);
state &= ((1ul << 31) | (1ul << 30) | (1ul << 0));
status = acpi_video_device_set_state(dev, state);
--
Greetings, Michael.
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