[PATCH bpf] libbpf: Fix OOB read in btf_dump_get_bitfield_value

[Varun R Mallya <varunrmallya@gmail.com>]

When dumping bitfield data, btf_dump_get_bitfield_value() reads data
based on the underlying type's size (t->size). However, it does not
verify that the provided data buffer (data_sz) is large enough to
contain these bytes.

If btf_dump__dump_type_data() is called with a buffer smaller than
the type's size, this leads to an out-of-bounds read. This was
confirmed by AddressSanitizer in the linked issue.

Fix this by ensuring we do not read past the provided data_sz limit.

Fixes: a1d3cc3c5eca ("libbpf: Avoid use of __int128 in typed dump display")
Reported-by: Harrison Green <harrisonmichaelgreen@gmail.com>
Closes: https://github.com/libbpf/libbpf/issues/928
Suggested-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
---
 tools/lib/bpf/btf_dump.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 6388392f49a0..53c6624161d7 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1762,9 +1762,18 @@ static int btf_dump_get_bitfield_value(struct btf_dump *d,
 	__u16 left_shift_bits, right_shift_bits;
 	const __u8 *bytes = data;
 	__u8 nr_copy_bits;
+	__u8 start_bit, nr_bytes;
 	__u64 num = 0;
 	int i;
 
+	/* Calculate how many bytes cover the bitfield */
+	start_bit = bits_offset % 8;
+	nr_bytes = (start_bit + bit_sz + 7) / 8;
+
+	/* Bound check */
+	if (data + nr_bytes > d->typed_dump->data_end)
+		return -E2BIG;
+
 	/* Maximum supported bitfield size is 64 bits */
 	if (t->size > 8) {
 		pr_warn("unexpected bitfield size %d\n", t->size);
-- 
2.52.0