diff mbox series

[v3] bpf: core: fix shift-out-of-bounds in ___bpf_prog_run

Message ID 20210602212726.7-1-fuzzybritches0@gmail.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series [v3] bpf: core: fix shift-out-of-bounds in ___bpf_prog_run | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Kurt Manucredo June 2, 2021, 9:27 p.m. UTC 
UBSAN: shift-out-of-bounds in kernel/bpf/core.c:1414:2
shift exponent 248 is too large for 32-bit type 'unsigned int'

Reported-and-tested-by: syzbot+bed360704c521841c85d@syzkaller.appspotmail.com
Signed-off-by: Kurt Manucredo <fuzzybritches0@gmail.com>
---

https://syzkaller.appspot.com/bug?id=edb51be4c9a320186328893287bb30d5eed09231

Changelog:
----------
v3 - Make it clearer what the fix is for.
v2 - Fix shift-out-of-bounds in ___bpf_prog_run() by adding boundary
check in check_alu_op() in verifier.c.
v1 - Fix shift-out-of-bounds in ___bpf_prog_run() by adding boundary
check in ___bpf_prog_run().

Hi everyone,

I hope this fixes it!

kind regards

 kernel/bpf/verifier.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

Comments

Greg KH June 3, 2021, 4:43 a.m. UTC | #1 
On Wed, Jun 02, 2021 at 09:27:26PM +0000, Kurt Manucredo wrote:
> UBSAN: shift-out-of-bounds in kernel/bpf/core.c:1414:2
> shift exponent 248 is too large for 32-bit type 'unsigned int'

I'm sorry, but I still do not understand what this changelog text means.

Please be very descriptive about what you are doing and why you are
doing it.  All that is here is a message from a random tool :(

thanks,
greg k-h
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 94ba5163d4c5..04e3bf344ecd 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7880,13 +7880,25 @@  static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 			return -EINVAL;
 		}
 
-		if ((opcode == BPF_LSH || opcode == BPF_RSH ||
-		     opcode == BPF_ARSH) && BPF_SRC(insn->code) == BPF_K) {
+		if (opcode == BPF_LSH || opcode == BPF_RSH ||
+		     opcode == BPF_ARSH) {
 			int size = BPF_CLASS(insn->code) == BPF_ALU64 ? 64 : 32;
 
-			if (insn->imm < 0 || insn->imm >= size) {
-				verbose(env, "invalid shift %d\n", insn->imm);
-				return -EINVAL;
+			if (BPF_SRC(insn->code) == BPF_K) {
+				if (insn->imm < 0 || insn->imm >= size) {
+					verbose(env, "invalid shift %d\n", insn->imm);
+					return -EINVAL;
+				}
+			}
+			if (BPF_SRC(insn->code) == BPF_X) {
+				struct bpf_reg_state *src_reg;
+
+				src_reg = &regs[insn->src_reg];
+				if (src_reg->umax_value >= size) {
+					verbose(env, "invalid shift %lld\n",
+							src_reg->umax_value);
+					return -EINVAL;
+				}
 			}
 		}