bpf: Reject %p% format string in bprintf-like helpers

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Reject %p% format string in bprintf-like helpers static const char fmt[] = "%p%"; bpf_trace_printk(fmt, sizeof(fmt)); The above BPF program isn't rejected and causes a kernel warning at runtime: Please remove unsupported %\x00 in format string WARNING: CPU: 1 PID: 7244 at lib/vsprintf.c:2680 format_decode+0x49c/0x5d0 This happens because bpf_bprintf_prepare skips over the second %, detected as punctuation, while processing %p. This patch fixes it by not skipping over punctuation. %\x00 is then processed in the next iteration and rejected.

References

• https://git.kernel.org/stable/c/97303e541e12f1fea97834ec64b98991e8775f39
• https://git.kernel.org/stable/c/61d5fa45ed13e42af14c7e959baba9908b8ee6d4
• https://git.kernel.org/stable/c/e7be679124bae8cf4fa6e40d7e1661baddfb3289
• https://git.kernel.org/stable/c/6952aeace93f8c9ea01849efecac24dd3152c9c9
• https://git.kernel.org/stable/c/1c5f5fd47bbda17cb885fe6f03730702cd53d3f8
• https://git.kernel.org/stable/c/f8242745871f81a3ac37f9f51853d12854fd0b58