libbpf: Fix OOB read in btf_dump_get_bitfield_value

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>
Suggested-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260106233527.163487-1-varunrmallya@gmail.com
Closes: https://github.com/libbpf/libbpf/issues/928

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 6388392f49a0b5651ac92098eb02b7d080d542a2..53c6624161d79738b842e0310340816950c4498c 100644 (file)
--- 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);