[PATCH 6.4 107/800] libbpf: btf_dump_type_data_check_overflow needs to consider BTF_MEMBER_BITFIELD_SIZE

Greg Kroah-Hartman
2023-07-16T19:57:51Z

From: Martin KaFai Lau <martin.lau@kernel.org>

[ Upstream commit c39028b333f3a3a765c5c0b9726b8e38aedf0ba1 ]

The btf_dump/struct_data selftest is failing with:

[...]
test_btf_dump_struct_data:FAIL:unexpected return value dumping fs_context unexpected unexpected return value dumping fs_context: actual -7 != expected 264
[...]

The reason is in btf_dump_type_data_check_overflow(). It does not use
BTF_MEMBER_BITFIELD_SIZE from the struct's member (btf_member). Instead,
it is using the enum size which is 4. It had been working till the recent
commit 4e04143c869c ("fs_context: drop the unused lsm_flags member")
removed an integer member which also removed the 4 bytes padding at the
end of the fs_context. Missing this 4 bytes padding exposed this bug. In
particular, when btf_dump_type_data_check_overflow() reaches the member
'phase', -E2BIG is returned.

The fix is to pass bit_sz to btf_dump_type_data_check_overflow(). In
btf_dump_type_data_check_overflow(), it does a different size check when
bit_sz is not zero.

The current fs_context:

[3600] ENUM 'fs_context_purpose' encoding=UNSIGNED size=4 vlen=3
'FS_CONTEXT_FOR_MOUNT' val=0
'FS_CONTEXT_FOR_SUBMOUNT' val=1
'FS_CONTEXT_FOR_RECONFIGURE' val=2
[3601] ENUM 'fs_context_phase' encoding=UNSIGNED size=4 vlen=7
'FS_CONTEXT_CREATE_PARAMS' val=0
'FS_CONTEXT_CREATING' val=1
'FS_CONTEXT_AWAITING_MOUNT' val=2
'FS_CONTEXT_AWAITING_RECONF' val=3
'FS_CONTEXT_RECONF_PARAMS' val=4
'FS_CONTEXT_RECONFIGURING' val=5
'FS_CONTEXT_FAILED' val=6
[3602] STRUCT 'fs_context' size=264 vlen=21
'ops' type_id=3603 bits_offset=0
'uapi_mutex' type_id=235 bits_offset=64
'fs_type' type_id=872 bits_offset=1216
'fs_private' type_id=21 bits_offset=1280
'sget_key' type_id=21 bits_offset=1344
'root' type_id=781 bits_offset=1408
'user_ns' type_id=251 bits_offset=1472
'net_ns' type_id=984 bits_offset=1536
'cred' type_id=1785 bits_offset=1600
'log' type_id=3621 bits_offset=1664
'source' type_id=42 bits_offset=1792
'security' type_id=21 bits_offset=1856
's_fs_info' type_id=21 bits_offset=1920
'sb_flags' type_id=20 bits_offset=1984
'sb_flags_mask' type_id=20 bits_offset=2016
's_iflags' type_id=20 bits_offset=2048
'purpose' type_id=3600 bits_offset=2080 bitfield_size=8
'phase' type_id=3601 bits_offset=2088 bitfield_size=8
'need_free' type_id=67 bits_offset=2096 bitfield_size=1
'global' type_id=67 bits_offset=2097 bitfield_size=1
'oldapi' type_id=67 bits_offset=2098 bitfield_size=1

Fixes: 920d16af9b42 ("libbpf: BTF dumper support for typed data")
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20230428013638.1581263-1-martin.lau@linux.dev
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/btf_dump.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 580985ee55458..4d9f30bf7f014 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -2250,9 +2250,25 @@ static int btf_dump_type_data_check_overflow(struct btf_dump *d,
const struct btf_type *t,
__u32 id,
const void *data,
- __u8 bits_offset)
+ __u8 bits_offset,
+ __u8 bit_sz)
{
- __s64 size = btf__resolve_size(d->btf, id);
+ __s64 size;
+
+ if (bit_sz) {
+ /* bits_offset is at most 7. bit_sz is at most 128. */
+ __u8 nr_bytes = (bits_offset + bit_sz + 7) / 8;
+
+ /* When bit_sz is non zero, it is called from
+ * btf_dump_struct_data() where it only cares about
+ * negative error value.
+ * Return nr_bytes in success case to make it
+ * consistent as the regular integer case below.
+ */
+ return data + nr_bytes > d->typed_dump->data_end ? -E2BIG : nr_bytes;
+ }
+
+ size = btf__resolve_size(d->btf, id);

if (size < 0 || size >= INT_MAX) {
pr_warn("unexpected size [%zu] for id [%u]\n",
@@ -2407,7 +2423,7 @@ static int btf_dump_dump_type_data(struct btf_dump *d,
{
int size, err = 0;

- size = btf_dump_type_data_check_overflow(d, t, id, data, bits_offset);
+ size = btf_dump_type_data_check_overflow(d, t, id, data, bits_offset, bit_sz);
if (size < 0)
return size;
err = btf_dump_type_data_check_zero(d, t, id, data, bits_offset, bit_sz);
--
2.39.2