Common Bug Patterns in iproute2

Common Bug Patterns in iproute2

Argument Parsing Bugs

Using matches() in New Code

Bug: Using matches() instead of strcmp() for argument comparison.

Why it's wrong: The matches() function allows abbreviations, which can cause unexpected behavior when new arguments are added that share a prefix.

Example (BAD):

if (matches(*argv, "device") == 0) {  /* Matches "d", "de", "dev", etc. */

Example (GOOD):

if (strcmp(*argv, "device") == 0) {  /* Only matches "device" exactly */

Missing NEXT_ARG()

Bug: Forgetting to call NEXT_ARG() after accepting a keyword.

Example (BAD):

if (strcmp(*argv, "mtu") == 0) {
    mtu = atoi(*argv);  /* Still pointing at "mtu", not the value! */
}

Example (GOOD):

if (strcmp(*argv, "mtu") == 0) {
    NEXT_ARG();
    mtu = atoi(*argv);
}

JSON Output Bugs

Missing close_json_object()

Bug: Opening a JSON object but not closing it.

open_json_object("link");
print_string(PRINT_ANY, "name", "%s", name);
/* Missing: close_json_object(); */

Error Messages to stdout

Bug: Using printf() or fprintf(stdout, ...) for error messages.

Why it's wrong: Corrupts JSON output when -json flag is used.

Example (BAD):

printf("Error: invalid argument\n");

Example (GOOD):

fprintf(stderr, "Error: invalid argument\n");

Using fprintf for Display Output

Bug: Using fprintf(fp, ...) instead of print_XXX() helpers.

Example (BAD):

fprintf(fp, "mtu %u ", mtu);

Example (GOOD):

print_uint(PRINT_ANY, "mtu", "mtu %u ", mtu);

Memory Bugs

Missing NULL Check

Bug: Not checking malloc return value.

char *buf = malloc(size);
strcpy(buf, src);  /* Crash if malloc failed! */

Memory Leak on Error Path

Bug: Returning early without freeing allocated memory.

char *buf = malloc(size);
if (some_error) {
    return -1;  /* Leaks buf! */
}

Fix: Use goto for centralized cleanup.

Netlink Bugs

Missing Nested Attribute End

Bug: Opening a nested attribute but not closing it.

addattr_nest(&req.n, sizeof(req), IFLA_PROP_LIST);
addattr_l(&req.n, sizeof(req), IFLA_ALT_IFNAME, name, strlen(name) + 1);
/* Missing: addattr_nest_end(&req.n, proplist); */

Ignoring Netlink Errors

Bug: Not checking return value from netlink operations.

rtnl_talk(&rth, &req.n, NULL);  /* Ignoring return value! */

String Handling Bugs

Breaking User-Visible Strings

Bug: Splitting strings that users might grep for.

Example (BAD):

fprintf(stderr, "Error: could not find "
                "device\n");

Example (GOOD):

fprintf(stderr, "Error: could not find device\n");

Kernel Compatibility Bugs

Assuming Feature Exists

Bug: Using a kernel feature without checking if it's available.

Fix: Check return values, handle EOPNOTSUPP gracefully.

uapi Update Without Reference

Bug: Updating uapi headers without referencing the upstream kernel commit.

Fix: Always include the kernel commit hash in the patch description.