CVE-2025-37923: tracing: Fix oob write in trace_seq_to_buffer()

In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix oob write in traceseqtobuffer()

syzbot reported this bug: ================================================================== BUG: KASAN: slab-out-of-bounds in traceseqtobuffer kernel/trace/trace.c:1830 [inline] BUG: KASAN: slab-out-of-bounds in tracingsplicereadpipe+0x6be/0xdd0 kernel/trace/trace.c:6822 Write of size 4507 at addr ffff888032b6b000 by task syz.2.320/7260

CPU: 1 UID: 0 PID: 7260 Comm: syz.2.320 Not tainted 6.15.0-rc1-syzkaller-00301-g3bde70a2c827 #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025 Call Trace: <TASK> dumpstack lib/dumpstack.c:94 [inline] dumpstacklvl+0x116/0x1f0 lib/dumpstack.c:120 printaddressdescription mm/kasan/report.c:408 [inline] printreport+0xc3/0x670 mm/kasan/report.c:521 kasanreport+0xe0/0x110 mm/kasan/report.c:634 checkregioninline mm/kasan/generic.c:183 [inline] kasancheckrange+0xef/0x1a0 mm/kasan/generic.c:189 asanmemcpy+0x3c/0x60 mm/kasan/shadow.c:106 traceseqtobuffer kernel/trace/trace.c:1830 [inline] tracingsplicereadpipe+0x6be/0xdd0 kernel/trace/trace.c:6822 .... ==================================================================

It has been reported that traceseqtobuffer() tries to copy more data than PAGESIZE to buf. Therefore, to prevent this, we should use the smaller of traceseqused(&iter->seq) and PAGESIZE as an argument.