Executing xfs/104 test in a loop on Linux-v4.13 kernel on a ppc64
machine can cause the following NULL pointer dereference,
.queue_work_on+0x4c/0x80
.iomap_dio_bio_end_io+0xbc/0x1f0
.bio_endio+0x118/0x1f0
.blk_update_request+0xd0/0x470
.blk_mq_end_request+0x24/0xc0
.lo_complete_rq+0x40/0xe0
.__blk_mq_complete_request_remote+0x28/0x40
.flush_smp_call_function_queue+0xc4/0x1e0
.smp_ipi_demux_relaxed+0x8c/0x100
.icp_hv_ipi_action+0x54/0xa0
.__handle_irq_event_percpu+0x84/0x2c0
.handle_irq_event_percpu+0x28/0x80
.handle_percpu_irq+0x78/0xc0
.generic_handle_irq+0x40/0x70
.__do_irq+0x88/0x200
.call_do_irq+0x14/0x24
.do_IRQ+0x84/0x130
This occurs due to the following sequence of events,
1. Allocate dio for Direct I/O write.
2. Invoke iomap_apply() until iov_iter_count() bytes have been submitted.
- Assume that we have submitted atleast one bio. Hence iomap_dio->ref value
will be >= 2.
- If during the second iteration, iomap_apply() ends up returning -ENOSPC, we would
break out of the loop and since the 'ret' value is a negative number we
end up not allocating memory for super_block->s_dio_done_wq.
3. Meanwhile, iomap_dio_bio_end_io() is invoked for bios that have been
submitted and here the code ends up dereferencing the NULL pointer stored
at super_block->s_dio_done_wq.
This commit fixes the bug by allocating memory for
super_block->s_dio_done_wq before iomap_apply() is invoked.
Reported-by: Eryu Guan <eguan@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Tested-by: Eryu Guan <eguan@xxxxxxxxxx>
Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
---
Changelog:
v1->v2:
1. Fix indentation for the continuation of the if conditional.
v2->v3:
1. Remove architecture specific register dumps from the stack trace.
fs/iomap.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/fs/iomap.c b/fs/iomap.c
index 269b24a..d4f526a 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -993,6 +993,13 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
WARN_ON_ONCE(ret);
ret = 0;
+ if (iov_iter_rw(iter) == WRITE && !is_sync_kiocb(iocb) &&
+ !inode->i_sb->s_dio_done_wq) {
+ ret = sb_init_dio_done_wq(inode->i_sb);
+ if (ret < 0)
+ goto out_free_dio;
+ }
+
inode_dio_begin(inode);
blk_start_plug(&plug);
@@ -1015,13 +1022,6 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
if (ret < 0)
iomap_dio_set_error(dio, ret);
- if (ret >= 0 && iov_iter_rw(iter) == WRITE && !is_sync_kiocb(iocb) &&
- !inode->i_sb->s_dio_done_wq) {
- ret = sb_init_dio_done_wq(inode->i_sb);
- if (ret < 0)
- iomap_dio_set_error(dio, ret);
- }
-
if (!atomic_dec_and_test(&dio->ref)) {
if (!is_sync_kiocb(iocb))
return -EIOCBQUEUED;
--
2.9.5
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