src: Handle negative snprintf return values properly

Currently the BUFFER_SIZE macro doesn't take negative 'ret' values into
account. A negative return should just be passed through to the caller,
snprintf will already have set 'errno' properly.

Signed-off-by: Daniel Gröber <dxld@darkboxed.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 6 insertions, 3 deletions

diff --git a/src/conntrack/api.c b/src/conntrack/api.c
index ffa5216..78d7d61 100644
--- a/src/conntrack/api.c
+++ b/src/conntrack/api.c
@@ -1099,9 +1099,9 @@ int nfct_catch(struct nfct_handle *h)
  * print the message just after you receive the destroy event. If you want
  * more accurate timestamping, use NFCT_OF_TIMESTAMP.
  *
- * This function returns the size of the information that _would_ have been 
- * written to the buffer, even if there was no room for it. Thus, the
- * behaviour is similar to snprintf.
+ * On error, -1 is returned and errno is set appropiately. Otherwise the
+ * size of what _would_ be written is returned, even if the size of the
+ * buffer is insufficient. This behaviour is similar to snprintf.
  */
 int nfct_snprintf(char *buf,
 		  unsigned int size,
diff --git a/src/conntrack/snprintf.c b/src/conntrack/snprintf.c
index 17ad885..eb26af4 100644
--- a/src/conntrack/snprintf.c
+++ b/src/conntrack/snprintf.c
@@ -85,6 +85,9 @@ int __snprintf_conntrack(char *buf,
 		return -1;
 	}
 
+	if (size < 0)
+		return size;
+
 	/* NULL terminated string */
 	buf[size+1 > len ? len-1 : size] = '\0';