• Rabin Vincent's avatar
    splice: handle zero nr_pages in splice_to_pipe() · d6785d91
    Rabin Vincent authored
    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)
    
    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@vger.kernel.org
    Signed-off-by: default avatarRabin Vincent <rabin@rab.in>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    d6785d91
splice.c 46.2 KB