bpf: Skip scalar adjustment for BPF_NEG if dst is a pointer

In check_alu_op(), the verifier currently calls check_reg_arg() and
adjust_scalar_min_max_vals() unconditionally for BPF_NEG operations.
However, if the destination register holds a pointer, these scalar
adjustments are unnecessary and potentially incorrect.

This patch adds a check to skip the adjustment logic when the destination
register contains a pointer.

Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=d36d5ae81e1b0a53ef58
Fixes: aced132 ("bpf: Add range tracking for BPF_NEG")
Suggested-by: KaFai Wan <[email protected]>
Suggested-by: Eduard Zingerman <[email protected]>
Signed-off-by: Brahmajit Das <[email protected]>

Author: listout

kernel/bpf/verifier.c

@@ -15645,7 +15645,8 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 		}
 
 		/* check dest operand */
-		if (opcode == BPF_NEG) {
+		if (opcode == BPF_NEG &&
+		    regs[insn->dst_reg].type == SCALAR_VALUE) {
 			err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
 			err = err ?: adjust_scalar_min_max_vals(env, insn,
 							 &regs[insn->dst_reg],