linux-kernel - [PATCH 5.6 020/254] null_blk: Suppress an UBSAN complaint triggered when setting memory

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Date:   Thu, 16 Apr 2020 15:21:49 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bart Van Assche <bvanassche@....org>,
        Chaitanya Kulkarni <chaitanya.kulkarni@....com>,
        Johannes Thumshirn <jth@...nel.org>,
        Hannes Reinecke <hare@...e.com>,
        Ming Lei <ming.lei@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.6 020/254] null_blk: Suppress an UBSAN complaint triggered when setting memory_backed

From: Bart Van Assche <bvanassche@....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@....org>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@....com>
Cc: Johannes Thumshirn <jth@...nel.org>
Cc: Hannes Reinecke <hare@...e.com>
Cc: Ming Lei <ming.lei@...hat.com>
Cc: Christoph Hellwig <hch@...radead.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.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