[PATCH net v2] netfilter: Add protection for bmp length out of range

Lena Wang (王娜)
2024-03-01T15:12:31Z

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 get_bitmap uses the
length to make a shift operation. It will change into negative
after several loop.

UBSAN load can detect a negative shift as an undefined behaviour
and reports an exception.

So we should add the protection to avoid the length exceeding 32.
If it exceeds it will return out of range error and stop decoding
ras message.

Signed-off-by: Lena Wang <lena.wang@mediatek.com>
---
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)
--
2.18.0