On Thu, 10 Mar 2016 21:19:06 +0100 Rabin Vincent <rabin@xxxxxx> wrote: > Running the following command: > > busybox cat /sys/kernel/debug/tracing/trace_pipe > /dev/null > > with any tracing enabled pretty very quickly leads to various NULL > pointer dereferences and VM BUG_ON()s, such as these: > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000020 > IP: [<ffffffff8119df6c>] generic_pipe_buf_release+0xc/0x40 > Call Trace: > [<ffffffff811c48a3>] splice_direct_to_actor+0x143/0x1e0 > [<ffffffff811c42e0>] ? generic_pipe_buf_nosteal+0x10/0x10 > [<ffffffff811c49cf>] do_splice_direct+0x8f/0xb0 > [<ffffffff81196869>] do_sendfile+0x199/0x380 > [<ffffffff81197600>] SyS_sendfile64+0x90/0xa0 > [<ffffffff8192cbee>] entry_SYSCALL_64_fastpath+0x12/0x6d > > page dumped because: VM_BUG_ON_PAGE(atomic_read(&page->_count) == 0) > kernel BUG at include/linux/mm.h:367! > invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC > RIP: [<ffffffff8119df9c>] generic_pipe_buf_release+0x3c/0x40 > Call Trace: > [<ffffffff811c48a3>] splice_direct_to_actor+0x143/0x1e0 > [<ffffffff811c42e0>] ? generic_pipe_buf_nosteal+0x10/0x10 > [<ffffffff811c49cf>] do_splice_direct+0x8f/0xb0 > [<ffffffff81196869>] do_sendfile+0x199/0x380 > [<ffffffff81197600>] SyS_sendfile64+0x90/0xa0 > [<ffffffff8192cd1e>] tracesys_phase2+0x84/0x89 > > (busybox's cat uses sendfile(2), unlike the coreutils version) Ouch! > > This is because tracing_splice_read_pipe() can call splice_to_pipe() > with spd->nr_pages == 0. spd_pages underflows in splice_to_pipe() and > we fill the page pointers and the other fields of the pipe_buffers with > garbage. > > All other callers of splice_to_pipe() avoid calling it when nr_pages == > 0, and we could make tracing_splice_read_pipe() do that too, but it > seems reasonable to have splice_to_page() handle this condition > gracefully. > > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Rabin Vincent <rabin@xxxxxx> > --- I think this should definitely be applied, but it's not my code to apply it. I'll add this to make sure that trace_pipe is not the cause anymore: -- Steve diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 0ae46048f724..cb2b708e4ea7 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4954,7 +4954,10 @@ static ssize_t tracing_splice_read_pipe(struct file *filp, spd.nr_pages = i; - ret = splice_to_pipe(pipe, &spd); + if (i) + ret = splice_to_pipe(pipe, &spd); + else + ret = 0; out: splice_shrink_spd(&spd); return ret; -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
