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authorRabin Vincent <rabin@rab.in>2016-03-10 21:19:06 +0100
committerSasha Levin <sasha.levin@oracle.com>2016-04-18 08:49:36 -0400
commit0651623b0d2d44343184791e7145f0fe871eec6e (patch)
tree85cfc79a22fa9f4a8f196106e13c451eec7b14b9 /fs
parent53c83cddcf243ea06ce8b41b0328a2733b3aa88e (diff)
downloadlinux-linaro-stable-0651623b0d2d44343184791e7145f0fe871eec6e.tar.gz
splice: handle zero nr_pages in splice_to_pipe()
[ Upstream commit d6785d9152147596f60234157da2b02540c3e60f ] 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: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/splice.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/splice.c b/fs/splice.c
index 75c6058eabf2..cf0cb768a1a7 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -186,6 +186,9 @@ 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;