8000 splice: don't merge into linked buffers · torvalds/linux@1bdc347 · GitHub
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thejhgregkh
thejh
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gregkh
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splice: don't merge into linked buffers
commit a0ce2f0 upstream. Before this patch, it was possible for two pipes to affect each other after data had been transferred between them with tee(): ============ $ cat tee_test.c int main(void) { int pipe_a[2]; if (pipe(pipe_a)) err(1, "pipe"); int pipe_b[2]; if (pipe(pipe_b)) err(1, "pipe"); if (write(pipe_a[1], "abcd", 4) != 4) err(1, "write"); if (tee(pipe_a[0], pipe_b[1], 2, 0) != 2) err(1, "tee"); if (write(pipe_b[1], "xx", 2) != 2) err(1, "write"); char buf[5]; if (read(pipe_a[0], buf, 4) != 4) err(1, "read"); buf[4] = 0; printf("got back: '%s'\n", buf); } $ gcc -o tee_test tee_test.c $ ./tee_test got back: 'abxx' $ ============ As suggested by Al Viro, fix it by creating a separate type for non-mergeable pipe buffers, then changing the types of buffers in splice_pipe_to_pipe() and link_pipe(). Cc: <stable@vger.kernel.org> Fixes: 7c77f0b ("splice: implement pipe to pipe splicing") Fixes: 7052449 ("[PATCH] splice: add support for sys_tee()") Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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3 files changed

+19
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lines changed

3 files changed

+19
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lines changed

‎fs/pipe.c

+14
Original file line numberDiff line numberDiff line change
@@ -239,6 +239,14 @@ static const struct pipe_buf_operations anon_pipe_buf_ops = {
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.get = generic_pipe_buf_get,
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};
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static const struct pipe_buf_operations anon_pipe_buf_nomerge_ops = {
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.can_merge = 0,
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.confirm = generic_pipe_buf_confirm,
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.release = anon_pipe_buf_release,
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.steal = anon_pipe_buf_steal,
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.get = generic_pipe_buf_get,
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};
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static const struct pipe_buf_operations packet_pipe_buf_ops = {
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.can_merge = 0,
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.confirm = generic_pipe_buf_confirm,
@@ -247,6 +255,12 @@ static const struct pipe_buf_operations packet_pipe_buf_ops = {
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.get = generic_pipe_buf_get,
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};
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void pipe_buf_mark_unmergeable(struct pipe_buffer *buf)
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{
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if (buf->ops == &anon_pipe_buf_ops)
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buf->ops = &anon_pipe_buf_nomerge_ops;
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}
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static ssize_t
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pipe_read(struct kiocb *iocb, struct iov_iter *to)
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{

‎fs/splice.c

+4
Original file line numberDiff line numberDiff line change
@@ -1580,6 +1580,8 @@ static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
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*/
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obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
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pipe_buf_mark_unmergeable(obuf);
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obuf->len = len;
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opipe->nrbufs++;
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ibuf->offset += obuf->len;
@@ -1654,6 +1656,8 @@ static int link_pipe(struct pipe_inode_info *ipipe,
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*/
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obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
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pipe_buf_mark_unmergeable(obuf);
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if (obuf->len > len)
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obuf->len = len;
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‎include/linux/pipe_fs_i.h

+1
Original file line numberDiff line numberDiff line change
@@ -183,6 +183,7 @@ void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
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int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
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int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
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void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
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void pipe_buf_mark_unmergeable(struct pipe_buffer *buf);
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extern const struct pipe_buf_operations nosteal_pipe_buf_ops;
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