In the Linux kernel, the following vulnerability has been resolved:
tracing/dma: Cap dma_map_sg tracepoint arrays to prevent buffer overflow
The dma_map_sg tracepoint can trigger a perf buffer overflow when tracing large scatter-gather lists. With devices like virtio-gpu creating large DRM buffers, nents can exceed 1000 entries, resulting in:
phys_addrs: 1000 * 8 bytes = 8,000 bytes dma_addrs: 1000 * 8 bytes = 8,000 bytes lengths: 1000 * 4 bytes = 4,000 bytes Total: ~20,000 bytes
This exceeds PERF_MAX_TRACE_SIZE (8192 bytes), causing:
WARNING: CPU: 0 PID: 5497 at kernel/trace/trace_event_perf.c:405 perf buffer not large enough, wanted 24620, have 8192
Cap all three dynamic arrays at 128 entries using min() in the array size calculation. This ensures arrays are only as large as needed (up to the cap), avoiding unnecessary memory allocation for small operations while preventing overflow for large ones.
The tracepoint now records the full nents/ents counts and a truncated flag so users can see when data has been capped.
Changes in v2:
- Use min(nents, DMA_TRACE_MAX_ENTRIES) for dynamic array sizing
- This allocates only what's needed up to the cap, avoiding waste
Reviwed-by: Sean Anderson