Re: [PATCH net v3] netfilter: Add protection for bmp length out of range

["Lena Wang (王娜)" <Lena.Wang@mediatek.com>]

On Tue, 2024-03-05 at 19:25 +0800, lena wang wrote:
> From: Lena Wang <lena.wang@mediatek.com>
> 
> UBSAN load reports an exception of BRK#5515 SHIFT_ISSUE:Bitwise
> shifts
> that are out of bounds for their data type.
> 
> vmlinux   get_bitmap(b=75) + 712
> <net/netfilter/nf_conntrack_h323_asn1.c:0>
> vmlinux   decode_seq(bs=0xFFFFFFD008037000, f=0xFFFFFFD008037018,
> level=134443100) + 1956
> <net/netfilter/nf_conntrack_h323_asn1.c:592>
> vmlinux   decode_choice(base=0xFFFFFFD0080370F0, level=23843636) +
> 1216
> <net/netfilter/nf_conntrack_h323_asn1.c:814>
> vmlinux   decode_seq(f=0xFFFFFFD0080371A8, level=134443500) + 812
> <net/netfilter/nf_conntrack_h323_asn1.c:576>
> vmlinux   decode_choice(base=0xFFFFFFD008037280, level=0) + 1216
> <net/netfilter/nf_conntrack_h323_asn1.c:814>
> vmlinux   DecodeRasMessage() + 304
> <net/netfilter/nf_conntrack_h323_asn1.c:833>
> vmlinux   ras_help() + 684
> <net/netfilter/nf_conntrack_h323_main.c:1728>
> vmlinux   nf_confirm() + 188
> <net/netfilter/nf_conntrack_proto.c:137>
> 
> Due to abnormal data in skb->data, the extension bitmap length
> exceeds 32 when decoding ras message then uses the length to make
> a shift operation. It will change into negative after several loop.
> UBSAN load could detect a negative shift as an undefined behaviour
> and reports exception.
> So we add the protection to avoid the length exceeding 32. Or else
> it will return out of range error and stop decoding.
> 
> Fixes: 5e35941d9901 ("[NETFILTER]: Add H.323 conntrack/NAT helper")
> Signed-off-by: Lena Wang <lena.wang@mediatek.com>
> ---
> v3:
>   - add "Fixes:" tag.
> v2:
>   - add length protecton for another get_bitmap call.
>   - update commit message to trim stacktrace.
> ---
> ---
>  net/netfilter/nf_conntrack_h323_asn1.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/netfilter/nf_conntrack_h323_asn1.c
> b/net/netfilter/nf_conntrack_h323_asn1.c
> index e697a824b001..540d97715bd2 100644
> --- a/net/netfilter/nf_conntrack_h323_asn1.c
> +++ b/net/netfilter/nf_conntrack_h323_asn1.c
> @@ -533,6 +533,8 @@ static int decode_seq(struct bitstr *bs, const
> struct field_t *f,
>  	/* Get fields bitmap */
>  	if (nf_h323_error_boundary(bs, 0, f->sz))
>  		return H323_ERROR_BOUND;
> +	if (f->sz > 32)
> +		return H323_ERROR_RANGE;
>  	bmp = get_bitmap(bs, f->sz);
>  	if (base)
>  		*(unsigned int *)base = bmp;
> @@ -589,6 +591,8 @@ static int decode_seq(struct bitstr *bs, const
> struct field_t *f,
>  	bmp2_len = get_bits(bs, 7) + 1;
>  	if (nf_h323_error_boundary(bs, 0, bmp2_len))
>  		return H323_ERROR_BOUND;
> +	if (bmp2_len > 32)
> +		return H323_ERROR_RANGE;
>  	bmp2 = get_bitmap(bs, bmp2_len);
>  	bmp |= bmp2 >> f->sz;
>  	if (base)

Dear all,
the patch is not applied and it may be due to format error with
evolution. I will try to resend v4 version with git send-mail.

Could anyone help to change the v3 state to Change Requested?

Thanks
Lena