[PATCH AUTOSEL 5.6 20/68] null_blk: Suppress an UBSAN complaint triggered when setting 'memory_backed'

Sasha Levin
2020-04-10T03:47:05Z

From: Bart Van Assche <bvanassche@acm.org>

[ Upstream commit b9853b4d6fb403ccb1d4d82e2d39fc17fc07519c ]

Although it is not clear to me why UBSAN complains when 'memory_backed'
is set, this patch suppresses the UBSAN complaint that is triggered when
setting that configfs attribute.

UBSAN: Undefined behaviour in drivers/block/null_blk_main.c:327:1
load of value 16 is not a valid value for type '_Bool'
CPU: 2 PID: 8396 Comm: check Not tainted 5.6.0-rc1-dbg+ #14
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Call Trace:
dump_stack+0xa5/0xe6
ubsan_epilogue+0x9/0x26
__ubsan_handle_load_invalid_value+0x6d/0x76
nullb_device_memory_backed_store.cold+0x2c/0x38 [null_blk]
configfs_write_file+0x1c4/0x250 [configfs]
__vfs_write+0x4c/0x90
vfs_write+0x145/0x2c0
ksys_write+0xd7/0x180
__x64_sys_write+0x47/0x50
do_syscall_64+0x6f/0x2f0
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Cc: Johannes Thumshirn <jth@kernel.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/block/null_blk_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
index d5b4a92033d48..2b8b4cb447cfb 100644
--- a/drivers/block/null_blk_main.c
+++ b/drivers/block/null_blk_main.c
@@ -276,7 +276,7 @@ nullb_device_##NAME##_store(struct config_item *item, const char *page, \
{ \
int (*apply_fn)(struct nullb_device *dev, TYPE new_value) = APPLY;\
struct nullb_device *dev = to_nullb_device(item); \
- TYPE uninitialized_var(new_value); \
+ TYPE new_value = 0; \
int ret; \
\
ret = nullb_device_##TYPE##_attr_store(&new_value, page, count);\
--
2.20.1