[PATCH V2 iproute2-next] ip: ipmaddr.c: Fix possible integer underflow in read_igmp()

[PATCH V2 iproute2-next] ip: ipmaddr.c: Fix possible integer underflow in read_igmp()

[Anton Moryakov]

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

Re: [PATCH V2 iproute2-next] ip: ipmaddr.c: Fix possible integer underflow in read_igmp()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to iproute2/iproute2-next.git (main)
by David Ahern <dsahern@kernel.org>:

On Sun, 20 Jul 2025 18:38:43 +0300 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [V2,iproute2-next] ip: ipmaddr.c: Fix possible integer underflow in read_igmp()
    https://git.kernel.org/pub/scm/network/iproute2/iproute2-next.git/commit/?id=5734dc8aa703

You are awesome, thank you!
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