4.17-stable review patch. If anyone has any objections, please let me know.
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From: Wenwen Wang wang6495@umn.edu
commit bd23a7269834dc7c1f93e83535d16ebc44b75eba upstream.
In vbg_misc_device_ioctl(), the header of the ioctl argument is copied from the userspace pointer 'arg' and saved to the kernel object 'hdr'. Then the 'version', 'size_in', and 'size_out' fields of 'hdr' are verified.
Before this commit, after the checks a buffer for the entire request would be allocated and then all data including the verified header would be copied from the userspace 'arg' pointer again.
Given that the 'arg' pointer resides in userspace, a malicious userspace process can race to change the data pointed to by 'arg' between the two copies. By doing so, the user can bypass the verifications on the ioctl argument.
This commit fixes this by using the already checked copy of the header to fill the header part of the allocated buffer and only copying the remainder of the data from userspace.
Signed-off-by: Wenwen Wang wang6495@umn.edu Reviewed-by: Hans de Goede hdegoede@redhat.com Cc: Justin Forbes jmforbes@linuxtx.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/virt/vboxguest/vboxguest_linux.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/drivers/virt/vboxguest/vboxguest_linux.c +++ b/drivers/virt/vboxguest/vboxguest_linux.c @@ -121,7 +121,9 @@ static long vbg_misc_device_ioctl(struct if (!buf) return -ENOMEM;
- if (copy_from_user(buf, (void *)arg, hdr.size_in)) { + *((struct vbg_ioctl_hdr *)buf) = hdr; + if (copy_from_user(buf + sizeof(hdr), (void *)arg + sizeof(hdr), + hdr.size_in - sizeof(hdr))) { ret = -EFAULT; goto out; }