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Subject[PATCH 5.4 20/92] io_uring: fix dead-hung for non-iter fixed rw
Date
From: Pavel Begunkov <asml.silence@gmail.com>

commit 311ae9e159d81a1ec1cf645daf40b39ae5a0bd84 upstream.

Read/write requests to devices without implemented read/write_iter
using fixed buffers can cause general protection fault, which totally
hangs a machine.

io_import_fixed() initialises iov_iter with bvec, but loop_rw_iter()
accesses it as iovec, dereferencing random address.

kmap() page by page in this case

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/io_uring.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1351,9 +1351,19 @@ static ssize_t loop_rw_iter(int rw, stru
return -EAGAIN;

while (iov_iter_count(iter)) {
- struct iovec iovec = iov_iter_iovec(iter);
+ struct iovec iovec;
ssize_t nr;

+ if (!iov_iter_is_bvec(iter)) {
+ iovec = iov_iter_iovec(iter);
+ } else {
+ /* fixed buffers import bvec */
+ iovec.iov_base = kmap(iter->bvec->bv_page)
+ + iter->iov_offset;
+ iovec.iov_len = min(iter->count,
+ iter->bvec->bv_len - iter->iov_offset);
+ }
+
if (rw == READ) {
nr = file->f_op->read(file, iovec.iov_base,
iovec.iov_len, &kiocb->ki_pos);
@@ -1362,6 +1372,9 @@ static ssize_t loop_rw_iter(int rw, stru
iovec.iov_len, &kiocb->ki_pos);
}

+ if (iov_iter_is_bvec(iter))
+ kunmap(iter->bvec->bv_page);
+
if (nr < 0) {
if (!ret)
ret = nr;

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