iomap: don't resubmit an ioend after ->writeback_submit() failed

iomap_add_to_ioend() submits the pending ioend through
->writeback_submit() before allocating a new one for the current range.
When the submission fails the helper completes the ioend with an error,
but iomap_add_to_ioend() returns the error without clearing
wpc->wb_ctx.  iomap_writepages() then submits whatever wpc->wb_ctx
points to, so the already completed ioend is submitted a second time.

For XFS the second bio_endio() lands in xfs_end_bio(), which
list_add_tail()s the already linked ioend into ip->i_ioend_list.  This
corrupts the list and leaves a use-after-free/double-free window against
the ioend completion worker.  Reproduced with a fault-injected
->writeback_submit() failure on a reflinked XFS file with several
CoW writeback ranges in flight: the unfixed kernel hits repeated
"list_add double add" warnings from __list_add_valid_or_report(),
the fixed kernel fails writeback cleanly.

Clear wpc->wb_ctx when ->writeback_submit() fails.  The old
iomap_submit_ioend() cleared the context unconditionally; that clear was
lost when submission moved to iomap_ioend_writeback_submit().  The final
->writeback_submit() call in iomap_writepages() needs no equivalent fix:
it is the last thing the function does before returning, and every
caller allocates its iomap_writepage_ctx on the stack for a single call,
so wpc->wb_ctx is never read again afterwards.

Fixes: f4fa7981fa26 ("iomap: hide ioends from the generic writeback code")
Cc: stable@vger.kernel.org # v6.17
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Link: https://patch.msgid.link/90fbd42df4f51306e57a95830d2d53873f630eb9.1790342457.git.parri.andrea@gmail.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions