Sorry, this patch is wrong, please ignore. On Mon, 2025-10-27 at 00:38 +0800, KaFai Wan wrote: > Syzbot reported a kernel warning due to a range invariant violation in > the BPF verifier. The issue occurs when tnum_overlap() fails to detect > that two tnums don't have any overlapping bits. > > The problematic BPF program: > 0: call bpf_get_prandom_u32 > 1: r6 = r0 > 2: r6 &= 0xFFFFFFFFFFFFFFF0 > 3: r7 = r0 > 4: r7 &= 0x07 > 5: r7 -= 0xFF > 6: if r6 == r7 goto <exit> > > After instruction 5, R7 has the range: > R7: u64=[0xffffffffffffff01, 0xffffffffffffff08] > var_off=(0xffffffffffffff00; 0xf) > > R6 and R7 don't overlap since they have no agreeing bits. However, > is_branch_taken() fails to recognize this, causing the verifier to > refine register bounds and end up with inconsistent bounds: > > 6: if r6 == r7 goto <exit> > R6: u64=[0xffffffffffffff01, 0xffffffffffffff00] > var_off=(0xffffffffffffff00, 0x0) > R7: u64=[0xffffffffffffff01, 0xffffffffffffff00] > var_off=(0xffffffffffffff00, 0x0) > > The root cause is that tnum_overlap() doesn't properly handle the case > where the masks have no overlapping bits. > > Fix this by adding an early check for zero mask intersection in > tnum_overlap(). > > Reported-by: [email protected] > Fixes: f41345f47fb2 ("bpf: Use tnums for JEQ/JNE is_branch_taken logic") > Signed-off-by: KaFai Wan <[email protected]> > --- > kernel/bpf/tnum.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/bpf/tnum.c b/kernel/bpf/tnum.c > index f8e70e9c3998..af2f38b4f840 100644 > --- a/kernel/bpf/tnum.c > +++ b/kernel/bpf/tnum.c > @@ -163,6 +163,8 @@ bool tnum_overlap(struct tnum a, struct tnum b) > { > u64 mu; > > + if ((a.mask & b.mask) == 0) > + return false; > mu = ~a.mask & ~b.mask; > return (a.value & mu) == (b.value & mu); > }
-- Thanks, KaFai
