On 2020/9/28 19:48, Dan Carpenter wrote:
On Mon, Sep 28, 2020 at 06:48:38PM +0800, Jing Xiangfeng wrote:In try_start_dim_transfer(), pointer hdm_ch is accessed before checking. This may lead to a potential null pointer dereference. Fix this by dereferencing hdm_ch after calling BUG_ON(). Signed-off-by: Jing Xiangfeng <jingxiangfeng@xxxxxxxxxx> --- drivers/staging/most/dim2/dim2.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/staging/most/dim2/dim2.c b/drivers/staging/most/dim2/dim2.c index 509c8012d20b..ccd7cc7545e4 100644 --- a/drivers/staging/most/dim2/dim2.c +++ b/drivers/staging/most/dim2/dim2.c @@ -148,7 +148,7 @@ void dimcb_on_error(u8 error_id, const char *error_message) static int try_start_dim_transfer(struct hdm_channel *hdm_ch) { u16 buf_size; - struct list_head *head = &hdm_ch->pending_list;This is not a dereference, it's just pointer math. In other words: struct list_head *head = hdm_ch + offsetof(struct hdm_channel, pending_list);
Thanks for correcting!
So the commit message is wrong because this cannot lead to a NULL dereference. It's better to just delete the BUG_ON(). We don't really like BUG_ON(). Checkpatch will complain about them. An Oops gives basically the same information as a BUG_ON() without completely killing the kernel so just dereferencing a NULL is preferable. Finally, we can see from the callers that "hdm_ch" is never NULL. regards, dan carpenter .
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