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@xxxxxxxxxxxxxxx Signed-off-by: Rabin Vincent <rabin@xxxxxx> --- fs/splice.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/splice.c b/fs/splice.c index 82bc0d64fc38..19e0b103d253 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -185,6 +185,9 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe, unsigned int spd_pages = spd->nr_pages; int ret, do_wakeup, page_nr; + if (!spd_pages) + return 0; + ret = 0; do_wakeup = 0; page_nr = 0; -- 2.7.0 -- 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
