[PATCH v2] tipc: Avoid copying bytes beyond the supplied data

[Chris Packham]

TLV_SET is called with a data pointer and a len parameter that tells us
how many bytes are pointed to by data. When invoking memcpy() we need
to careful to only copy len bytes.

Previously we would copy TLV_LENGTH(len) bytes which would copy an extra
4 bytes past the end of the data pointer which newer GCC versions
complain about.

 In file included from test.c:17:
 In function 'TLV_SET',
     inlined from 'test' at test.c:186:5:
 /usr/include/linux/tipc_config.h:317:3:
 warning: 'memcpy' forming offset [33, 36] is out of the bounds [0, 32]
 of object 'bearer_name' with type 'char[32]' [-Warray-bounds]
     memcpy(TLV_DATA(tlv_ptr), data, tlv_len);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 test.c: In function 'test':
 test.c::161:10: note:
 'bearer_name' declared here
     char bearer_name[TIPC_MAX_BEARER_NAME];
          ^~~~~~~~~~~

We still want to ensure any padding bytes at the end are initialised, do
this with a explicit memset() rather than copy bytes past the end of
data. Apply the same logic to TCM_SET.

Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
---

Changes in v2:
- Ensure padding bytes are initialised in both TLV_SET and TCM_SET

 include/uapi/linux/tipc_config.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/tipc_config.h b/include/uapi/linux/tipc_config.h
index 4b2c93b1934c..4955e1a9f1bc 100644
--- a/include/uapi/linux/tipc_config.h
+++ b/include/uapi/linux/tipc_config.h
@@ -307,8 +307,10 @@ static inline int TLV_SET(void *tlv, __u16 type, void *data, __u16 len)
 	tlv_ptr = (struct tlv_desc *)tlv;
 	tlv_ptr->tlv_type = htons(type);
 	tlv_ptr->tlv_len  = htons(tlv_len);
-	if (len && data)
-		memcpy(TLV_DATA(tlv_ptr), data, tlv_len);
+	if (len && data) {
+		memcpy(TLV_DATA(tlv_ptr), data, len);
+		memset(TLV_DATA(tlv_ptr) + len, 0, TLV_SPACE(len) - tlv_len);
+	}
 	return TLV_SPACE(len);
 }
 
@@ -405,8 +407,10 @@ static inline int TCM_SET(void *msg, __u16 cmd, __u16 flags,
 	tcm_hdr->tcm_len   = htonl(msg_len);
 	tcm_hdr->tcm_type  = htons(cmd);
 	tcm_hdr->tcm_flags = htons(flags);
-	if (data_len && data)
+	if (data_len && data) {
 		memcpy(TCM_DATA(msg), data, data_len);
+		memset(TCM_DATA(msg) + data_len, 0, TCM_SPACE(data_len) - msg_len);
+	}
 	return TCM_SPACE(data_len);
 }
 
-- 
2.21.0