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| author | Rabin Vincent <rabin@rab.in> | 2016-03-10 21:19:06 +0100 |
|---|---|---|
| committer | Willy Tarreau <w@1wt.eu> | 2016-06-07 10:42:46 +0200 |
| commit | 929522bfe429c0f9e834c93bdcb9e6a0292245cd (patch) | |
| tree | af3cfd2d1e7d3a9a67b6cd63c808e694bdf143b9 /fs | |
| parent | 9bd0caf31ca013ed42e4a00dd2872035975e5b04 (diff) | |
| download | lwn-929522bfe429c0f9e834c93bdcb9e6a0292245cd.tar.gz lwn-929522bfe429c0f9e834c93bdcb9e6a0292245cd.zip | |
splice: handle zero nr_pages in splice_to_pipe()
commit d6785d9152147596f60234157da2b02540c3e60f upstream.
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: Rabin Vincent <rabin@rab.in>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/splice.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/splice.c b/fs/splice.c index 3b94a6bba29f..2ffa7b0c62fd 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -189,6 +189,9 @@ 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; |