Re: [PATCH v2] libbpf: bounds-check float size in btf_dump_float_data()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

Pre-existing issues:
- [High] A malicious BTF can bypass size checks by defining a FLOAT or PTR member with a bitfield size, leading to an out-of-bounds memory read.
- [High] A mismatch between the target BTF alignment and the host architecture alignment requirements can cause an unaligned memory access crash when reading floats.
--

commit 8b775a18b4de3665e91e05ddb075a75dc6ae1b43
Author: Naveed Khan <naveed@digiscrypt.com>
Subject: libbpf: bounds-check float size in btf_dump_float_data()

This commit fixes a stack buffer overflow in btf_dump_float_data() by
validating the float size before copying it into an on-stack buffer. It also
changes the buffer to be 16-byte aligned so that valid long double floats
are always accepted.

> diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> index cc1ba65bb6c5a..dc26f3a160305 100644
> --- a/tools/lib/bpf/btf_dump.c
> +++ b/tools/lib/bpf/btf_dump.c
> @@ -1980,13 +1980,18 @@ static int btf_dump_float_data(struct btf_dump *d,
[ ... ]
>  	/* handle unaligned data; copy to local buffer */
>  	if (!ptr_is_aligned(d->btf, type_id, data)) {
> -		memcpy(&fl, data, sz);
> -		flp = &fl;
> +		memcpy(buf, data, sz);

[Severity: High]
This isn't a bug introduced by this patch, but could a malicious BTF bypass
size checks here by defining a FLOAT or PTR member with a bitfield size?

Looking at btf_dump_type_data_check_overflow(), it short-circuits the full
size bounds check against data_end when bit_sz != 0, checking only the
bitfield size:

    if (bit_sz) {
        __u8 nr_bytes = (bits_offset + bit_sz + 7) / 8;
        return data + nr_bytes > d->typed_dump->data_end ? -E2BIG : nr_bytes;
    }

However, we unconditionally read t->size bytes from data via memcpy
above, which could lead to an out-of-bounds heap read if the actual
data buffer is smaller than t->size.

> +		flp = (void *)buf;
>  	}
>  
>  	switch (sz) {

[Severity: High]
This is a pre-existing issue, but could this cause an unaligned memory
access crash on certain architectures when reading 16-byte floats?

ptr_is_aligned() checks alignment against the BTF target requirements,
which caps at 8 bytes. If the host architecture requires 16-byte
alignment for a 16-byte long double, and the data pointer is only
8-byte aligned, ptr_is_aligned() returns true and bypasses the local
buffer copy.

Later in the switch statement:

    case 16:
        btf_dump_type_values(d, "%Lf", flp->ld);

Casting that 8-byte aligned data pointer to union float_data and accessing
flp->ld could cause an unaligned memory access trap.

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Sashiko AI review · https://sashiko.dev/#/patchset/178229582410.80761.16669701451820050202@digiscrypt.com?part=1