fix a fencepost error in pipe_advance()
commit b9dc6f65bc5e232d1c05fe34b5daadc7e8bbf1fb upstream.
The logics in pipe_advance() used to release all buffers past the new
position failed in cases when the number of buffers to release was equal
to pipe->buffers. If that happened, none of them had been released,
leaving pipe full. Worse, it was trivial to trigger and we end up with
pipe full of uninitialized pages. IOW, it's an infoleak.
Reported-by: "Alan J. Wylie" <alan@wylie.me.uk>
Tested-by: "Alan J. Wylie" <alan@wylie.me.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index f2bd21b..efb0b4d 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -678,43 +678,50 @@
}
EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
-static void pipe_advance(struct iov_iter *i, size_t size)
+static inline void pipe_truncate(struct iov_iter *i)
{
struct pipe_inode_info *pipe = i->pipe;
- struct pipe_buffer *buf;
- int idx = i->idx;
- size_t off = i->iov_offset, orig_sz;
-
- if (unlikely(i->count < size))
- size = i->count;
- orig_sz = size;
-
- if (size) {
- if (off) /* make it relative to the beginning of buffer */
- size += off - pipe->bufs[idx].offset;
- while (1) {
- buf = &pipe->bufs[idx];
- if (size <= buf->len)
- break;
- size -= buf->len;
- idx = next_idx(idx, pipe);
- }
- buf->len = size;
- i->idx = idx;
- off = i->iov_offset = buf->offset + size;
- }
- if (off)
- idx = next_idx(idx, pipe);
if (pipe->nrbufs) {
- int unused = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
- /* [curbuf,unused) is in use. Free [idx,unused) */
- while (idx != unused) {
+ size_t off = i->iov_offset;
+ int idx = i->idx;
+ int nrbufs = (idx - pipe->curbuf) & (pipe->buffers - 1);
+ if (off) {
+ pipe->bufs[idx].len = off - pipe->bufs[idx].offset;
+ idx = next_idx(idx, pipe);
+ nrbufs++;
+ }
+ while (pipe->nrbufs > nrbufs) {
pipe_buf_release(pipe, &pipe->bufs[idx]);
idx = next_idx(idx, pipe);
pipe->nrbufs--;
}
}
- i->count -= orig_sz;
+}
+
+static void pipe_advance(struct iov_iter *i, size_t size)
+{
+ struct pipe_inode_info *pipe = i->pipe;
+ if (unlikely(i->count < size))
+ size = i->count;
+ if (size) {
+ struct pipe_buffer *buf;
+ size_t off = i->iov_offset, left = size;
+ int idx = i->idx;
+ if (off) /* make it relative to the beginning of buffer */
+ left += off - pipe->bufs[idx].offset;
+ while (1) {
+ buf = &pipe->bufs[idx];
+ if (left <= buf->len)
+ break;
+ left -= buf->len;
+ idx = next_idx(idx, pipe);
+ }
+ i->idx = idx;
+ i->iov_offset = buf->offset + left;
+ }
+ i->count -= size;
+ /* ... and discard everything past that point */
+ pipe_truncate(i);
}
void iov_iter_advance(struct iov_iter *i, size_t size)
@@ -774,6 +781,7 @@
size_t count)
{
BUG_ON(direction != ITER_PIPE);
+ WARN_ON(pipe->nrbufs == pipe->buffers);
i->type = direction;
i->pipe = pipe;
i->idx = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);