[PATCH iproute2-next] ip: ipmaddr.c: Fix possible integer underflow in read_igmp()

[Anton Moryakov <ant.v.moryakov@gmail.com>]

Static analyzer pointed out a potential error:

	Possible integer underflow: left operand is tainted. An integer underflow 
	may occur due to arithmetic operation (unsigned subtraction) between variable 
	'len' and value '1', when 'len' is tainted { [0, 18446744073709551615] }

The fix adds a check for 'len == 0' before accessing the last character of
the name, and skips the current line in such cases to avoid the underflow.

Reported-by: SVACE static analyzer
Signed-off-by: Anton Moryakov <ant.v.moryakov@gmail.com>
---
 ip/ipmaddr.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/ip/ipmaddr.c b/ip/ipmaddr.c
index 2418b303..2feb916a 100644
--- a/ip/ipmaddr.c
+++ b/ip/ipmaddr.c
@@ -150,6 +150,8 @@ static void read_igmp(struct ma_info **result_p)
 
 			sscanf(buf, "%d%s", &m.index, m.name);
 			len = strlen(m.name);
+			if(len == 0)
+				continue;
 			if (m.name[len - 1] == ':')
 				m.name[len - 1] = '\0';
 			continue;
-- 
2.39.2