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[posix] fix -Wstringop-truncation warning in IsLoopbackInterface (#13330)

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Address a CI build failure caused by a compiler warning promoted to an
error (`-Werror=stringop-truncation`) in POSIX mDNS socket management.

In `IsLoopbackInterface(int aIfIndex)` in `mdns_socket.cpp`, the
interface name was retrieved via `if_indextoname()` into `char
ifName[IF_NAMESIZE]` and then copied into `ifr.ifr_name` using:

    strncpy(ifr.ifr_name, ifName, sizeof(ifr.ifr_name) - 1);

Because both `ifName` and `ifr.ifr_name` are 16-byte arrays on Linux
(`IF_NAMESIZE == IFNAMSIZ`), calling `strncpy()` with a bound of 15
(`sizeof(ifr.ifr_name) - 1`) triggers `-Wstringop-truncation` on GCC
with fortified libc headers.

To resolve the warning and simplify the code, eliminate the temporary
`ifName` buffer and `strncpy()` copy by operating directly on `ifr`:

1. Zero-initialize `struct ifreq ifr` (`memset(&ifr, 0, sizeof(ifr))`)
   before checking the interface name.
2. Pass `ifr.ifr_name` directly (`char[IFNAMSIZ]`) as the destination
   buffer for `if_indextoname()`.
3. If `if_indextoname()` succeeds, `ifr.ifr_name` is NUL-terminated
   and can be checked via `strcmp(ifr.ifr_name, "lo") == 0`.
4. When the interface is not `"lo"`, `ifr` is already populated with
   the interface name and can be passed directly to `ioctl(fd,
   SIOCGIFFLAGS, &ifr)` to query the `IFF_LOOPBACK` flag.
This commit is contained in:
Jonathan Hui
2026-07-10 12:55:04 -07:00
committed by GitHub
parent 1860864511
commit f69d68f71a
1 changed files with 7 additions and 11 deletions
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src/posix/platform/mdns_socket.cpp
+7 -11
View File
@@ -462,10 +462,10 @@ exit:
#ifdef __linux__
static bool IsLoopbackInterface(int aIfIndex)
{
static int sLastIfIndex = -1;
static bool sLastIsLoopback = false;
bool isLoopback = false;
char ifName[IF_NAMESIZE];
static int sLastIfIndex = -1;
static bool sLastIsLoopback = false;
bool isLoopback = false;
struct ifreq ifr;
VerifyOrExit(aIfIndex > 0);
@@ -475,9 +475,10 @@ static bool IsLoopbackInterface(int aIfIndex)
ExitNow();
}
VerifyOrExit(if_indextoname(static_cast<unsigned int>(aIfIndex), ifName) != nullptr);
memset(&ifr, 0, sizeof(ifr));
VerifyOrExit(if_indextoname(static_cast<unsigned int>(aIfIndex), ifr.ifr_name) != nullptr);
if (strcmp(ifName, "lo") == 0)
if (strcmp(ifr.ifr_name, "lo") == 0)
{
isLoopback = true;
}
@@ -487,11 +488,6 @@ static bool IsLoopbackInterface(int aIfIndex)
if (fd >= 0)
{
struct ifreq ifr;
memset(&ifr, 0, sizeof(ifr));
strncpy(ifr.ifr_name, ifName, sizeof(ifr.ifr_name) - 1);
if (ioctl(fd, SIOCGIFFLAGS, &ifr) == 0)
{
isLoopback = ((ifr.ifr_flags & IFF_LOOPBACK) != 0);