Re: [PATCH] block/curl.c: Check error return from curl_easy_setopt()

[Hanna Reitz]

On 28.01.22 17:55, Peter Maydell wrote:
> Coverity points out that we aren't checking the return value
> from curl_easy_setopt() for any of the calls to it we make
> in block/curl.c.
>
> Fixes: Coverity CID 1459336, 1459482, 1460331
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> Big fat disclaimer: tested only with 'make check', which I suspect
> may not be exercising this block backend. Hints on how to test
> more thoroughly are welcome.
>
>   block/curl.c | 90 +++++++++++++++++++++++++++++++++-------------------
>   1 file changed, 58 insertions(+), 32 deletions(-)

One problem I see in general is that most of the setopt functions are 
(indirectly) called from `curl_open()`, which is supposed to return an 
error message.  Its `out` label seems to expect some error description 
in `state->errmsg`.  The error handling here doesn’t set such a description.

Then again, there are enough existing error paths that don’t set this 
description either, so it isn’t quite this patch’s duty to fix that 
situation.  I guess it would be nice if we had a wrapper for 
`curl_easy_setopt()` with an `Error **` parameter, so we could easily 
generate error messages that describe key and value (and then 
`curl_init_state()` should have an `Error **` parameter, too).

But this patch doesn’t make anything worse than it already is, so that’d 
rather be an idea for future clean-up.

> diff --git a/block/curl.c b/block/curl.c
> index 6a6cd729758..aaee1b17bef 100644
> --- a/block/curl.c
> +++ b/block/curl.c

[...]

> @@ -879,7 +902,10 @@ static void curl_setup_preadv(BlockDriverState *bs, 
> CURLAIOCB *acb)
>   
>       snprintf(state->range, 127, "%" PRIu64 "-%" PRIu64, start, end);
>       trace_curl_setup_preadv(acb->bytes, start, state->range);
> -    curl_easy_setopt(state->curl, CURLOPT_RANGE, state->range);
> +    if (curl_easy_setopt(state->curl, CURLOPT_RANGE, state->range)) {
> +        curl_clean_state(state);
> +        goto out;

I think we need to mark the request as failed by setting `acb->ret` to a 
negative value (and probably also clear `state->acb[0]` like the error 
path below does).

Hanna

> +    }
>   
>       if (curl_multi_add_handle(s->multi, state->curl) != CURLM_OK) {
>           state->acb[0] = NULL;