[PATCH bpf 0/2] bpf: Fix queue/stack map u32 index overflow

From: Yuan Chen <[email protected]>

queue/stack maps address their element storage with a u32 head/tail
index multiplied by value_size. The storage itself is allocated using
64-bit arithmetic, so a map with max_entries * value_size exceeding
U32_MAX can be created, and the u32 multiplication then wraps, making
push/peek/pop operate on the wrong element: map data gets corrupted and
stale values can leak to user space through peek.

The bound check that used to prevent this was removed by c85d69135a91
("bpf: move memory size checks to bpf_map_charge_init()"), which
migrated only the bytes-to-pages conversion and dropped the overflow
guard, so oversized queue/stack maps can be created again.

Patch 1 restores the bound at map creation time: a map whose element
storage would exceed U32_MAX bytes is rejected with -E2BIG, keeping the
u32 index multiplication overflow-free.
Patch 2 adds a regression test covering both map types and a
normal-sized control case.

Verification: built and run in QEMU - oversized queue/stack maps are
rejected with -E2BIG, normal-sized maps still work, and the
queue_stack_map selftest passes.

Yuan Chen (2):
  bpf: Fix queue/stack map u32 index overflow
  selftests/bpf: Add regression test for queue/stack map size limit

 kernel/bpf/queue_stack_maps.c                 |  7 ++++
 .../bpf/prog_tests/queue_stack_map.c          | 34 +++++++++++++++++++
 2 files changed, 41 insertions(+)

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2.54.0