netdev - [PATCH V2 iproute2-next] ip: ipmaddr.c: Fix possible integer underflow in read

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Message-Id: <20250720153843.62145-1-ant.v.moryakov@gmail.com>
Date: Sun, 20 Jul 2025 18:38:43 +0300
From: Anton Moryakov <ant.v.moryakov@...il.com>
To: netdev@...r.kernel.org
Cc: Anton Moryakov <ant.v.moryakov@...il.com>
Subject: [PATCH V2 iproute2-next] ip: ipmaddr.c: Fix possible integer underflow in read_igmp()

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@...il.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