On Mon, Oct 08, 2018 at 10:59:33AM +0200, Daniel Borkmann wrote:
From: Jann Horn jannh@google.com
[ upstream commit b799207e1e1816b09e7a5920fbb2d5fcf6edd681 ]
When I wrote commit 468f6eafa6c4 ("bpf: fix 32-bit ALU op verification"), I assumed that, in order to emulate 64-bit arithmetic with 32-bit logic, it is sufficient to just truncate the output to 32 bits; and so I just moved the register size coercion that used to be at the start of the function to the end of the function.
That assumption is true for almost every op, but not for 32-bit right shifts, because those can propagate information towards the least significant bit. Fix it by always truncating inputs for 32-bit ops to 32 bits.
Also get rid of the coerce_reg_to_size() after the ALU op, since that has no effect.
Applied, thanks.
greg k-h