{bp-19436} fix(net/igmp): restore General Query handling broken by pointer compare - #19619
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The group address in the IGMP header is declared as uint16_t grpaddr[2], so it decays to a pointer. Comparing it against INADDR_ANY compares the address of a struct member against 0, which is always false. The General Query branch is therefore unreachable and GCC discards it entirely. Commit 09bb292 ("net/igmp: fix build warning on GCC 12.2.0") replaced the original if (igmp->grpaddr == 0) with if (net_ipv4addr_cmp(igmp->grpaddr, INADDR_ANY) != 0) but net_ipv4addr_cmp(a, b) expands to (a == b) and INADDR_ANY expands to ((in_addr_t)0), so the emitted comparison is unchanged. The -Waddress diagnostic disappeared only because the comparison now originates inside a macro expanded from a header included via -isystem, and GCC suppresses warnings from system-header macros. The defect was hidden, not fixed. That commit also rewrote the unicast query test from group->grpaddr != 0, which was well-formed, into the same pointer comparison, making it unconditionally true. Convert the header field with net_ip4addr_conv32() once, and compare the resulting in_addr_t. The conversion was already being done in the group-specific branch, so this only hoists it and reuses it. Impact: a General Query (destination 224.0.0.1, group address 0) is the periodic query every IGMP querier sends. It currently falls through to the group-specific branch, where igmp_grpallocfind() allocates a group for 0.0.0.0 and schedules a report for it, while joined groups never have their report timers restarted. The querier then ages out the membership and multicast delivery to the device stops. Signed-off-by: Jacob Dahl <dahl.jakejacob@gmail.com>
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xiaoxiang781216
August 3, 2026 08:16
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Summary
The group address in the IGMP header is declared as uint16_t grpaddr[2], so it decays to a pointer. Comparing it against INADDR_ANY compares the address of a struct member against 0, which is always false. The General Query branch is therefore unreachable and GCC discards it entirely.
Commit 09bb292 ("net/igmp: fix build warning on GCC 12.2.0") replaced the original
with
but net_ipv4addr_cmp(a, b) expands to (a == b) and INADDR_ANY expands to ((in_addr_t)0), so the emitted comparison is unchanged. The -Waddress diagnostic disappeared only because the comparison now originates inside a macro expanded from a header included via -isystem, and GCC suppresses warnings from system-header macros. The defect was hidden, not fixed.
That commit also rewrote the unicast query test from group->grpaddr != 0, which was well-formed, into the same pointer comparison, making it unconditionally true.
Convert the header field with net_ip4addr_conv32() once, and compare the resulting in_addr_t. The conversion was already being done in the group-specific branch, so this only hoists it and reuses it.
Impact: a General Query (destination 224.0.0.1, group address 0) is the periodic query every IGMP querier sends. It currently falls through to the group-specific branch, where igmp_grpallocfind() allocates a group for 0.0.0.0 and schedules a report for it, while joined groups never have their report timers restarted. The querier then ages out the membership and multicast delivery to the device stops.
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