Re: [PATCH 10/21] hw/core: Fix latent fit_load_fdt() error handling bug

[Markus Armbruster <armbru@redhat.com>]

Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:

> 30.11.2019 22:42, Markus Armbruster wrote:
>> fit_load_fdt() recovers from fit_image_addr() failing with ENOENT.
>> Except it doesn't when its @errp argument is &error_fatal or
>> &error_abort, because it blindly passes @errp to fit_image_addr().
>> Messed up in commit 3eb99edb48 "loader-fit: Wean off error_printf()".
>> 
>> The bug can't bite as no caller actually passes &error_fatal or
>> &error_abort.  Fix it anyway.
>> 
>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>
> Hmm, actually it makes my
> "[PATCH v7 01/21] hw/core/loader-fit: fix freeing errp in fit_load_fdt"
> unnecessary. If you want you may drop my 01 (as it covers less problems),

Yes.

> and in this case you may note in your cover letter, that
> errp = NULL is broken here too (may be nobady pass it?),

You're right, null @errp is wrong, too.

> and normal errp is handled wrong, as *errp doesn't set to NULL after
> error_free(*errp)

Yes, that's wrong, too.  fit_load_fdt() itself doesn't use *errp after
freeing it, but it sets a trap for its callers.  

>                   (still, the only caller rely on return value more than on
> err, so the problem can't be triggered with current code)

True.

New commit message (based on v2's):

    hw/core: Fix fit_load_fdt() error API violations

    fit_load_fdt() passes @errp to fit_image_addr(), then recovers from
    ENOENT failures.  Passing @errp is wrong, because it works only as
    long as @errp is neither @error_fatal nor @error_abort.  Error
    recovery dereferences @errp.  That's also wrong; see the big comment
    in error.h.  Error recovery can leave *errp pointing to a freed
    Error object.  Wrong, it must be null on success.  Messed up in
    commit 3eb99edb48 "loader-fit: Wean off error_printf()".

    No caller actually passes such values, or uses *errp on success.

    Fix anyway: splice in a local Error *err, and error_propagate().

    Signed-off-by: Markus Armbruster <armbru@redhat.com>

Okay?

>
>> ---
>>   hw/core/loader-fit.c | 15 ++++++++-------
>>   1 file changed, 8 insertions(+), 7 deletions(-)
>> 
>> diff --git a/hw/core/loader-fit.c b/hw/core/loader-fit.c
>> index 953b16bc82..c465921b8f 100644
>> --- a/hw/core/loader-fit.c
>> +++ b/hw/core/loader-fit.c
>> @@ -178,11 +178,12 @@ static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
>>                           int cfg, void *opaque, const void *match_data,
>>                           hwaddr kernel_end, Error **errp)
>>   {
>> +    Error *err = NULL;
>>       const char *name;
>>       const void *data;
>>       const void *load_data;
>>       hwaddr load_addr;
>> -    int img_off, err;
>> +    int img_off;
>>       size_t sz;
>>       int ret;
>>   
>> @@ -197,13 +198,13 @@ static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
>>           return -EINVAL;
>>       }
>>   
>> -    err = fit_image_addr(itb, img_off, "load", &load_addr, errp);
>> -    if (err == -ENOENT) {
>> +    ret = fit_image_addr(itb, img_off, "load", &load_addr, &err);
>> +    if (ret == -ENOENT) {
>>           load_addr = ROUND_UP(kernel_end, 64 * KiB) + (10 * MiB);
>> -        error_free(*errp);
>> -    } else if (err) {
>> -        error_prepend(errp, "unable to read FDT load address from FIT: ");
>> -        ret = err;
>> +        error_free(err);
>> +    } else if (ret) {
>> +        error_propagate_prepend(errp, err,
>> +                                "unable to read FDT load address from FIT: ");
>>           goto out;
>>       }
>>   
>> 
>
> So much attention to that function :)
>
> I'd also propose the following:
>
> diff --git a/hw/core/loader-fit.c b/hw/core/loader-fit.c
> index c465921b8f..2c9efeef7a 100644
> --- a/hw/core/loader-fit.c
> +++ b/hw/core/loader-fit.c
> @@ -180,8 +180,8 @@ static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
>   {
>       Error *err = NULL;
>       const char *name;
> -    const void *data;
> -    const void *load_data;
> +    void *data;
> +    void *load_data;
>       hwaddr load_addr;
>       int img_off;
>       size_t sz;
> @@ -218,9 +218,9 @@ static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
>
>       ret = 0;
>   out:
> -    g_free((void *) data);
> +    g_free(data);
>       if (data != load_data) {
> -        g_free((void *) load_data);
> +        g_free(load_data);
>       }
>       return ret;
>   }
>
>
> Or, even better:
>
> --- a/hw/core/loader-fit.c
> +++ b/hw/core/loader-fit.c
> @@ -180,7 +180,8 @@ static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
>   {
>       Error *err = NULL;
>       const char *name;
> -    const void *data;
> +    g_autofree void *data = NULL;
> +    g_autofree void *fdt_filter_data = NULL;
>       const void *load_data;
>       hwaddr load_addr;
>       int img_off;
> @@ -202,27 +203,23 @@ static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
>       if (ret == -ENOENT) {
>           load_addr = ROUND_UP(kernel_end, 64 * KiB) + (10 * MiB);
>           error_free(err);
> +        return 0;
>       } else if (ret) {
>           error_propagate_prepend(errp, err,
>                                   "unable to read FDT load address from FIT: ");
> -        goto out;
> +        return ret;
>       }
>
>       if (ldr->fdt_filter) {
> -        load_data = ldr->fdt_filter(opaque, data, match_data, &load_addr);
> +        load_data = fdt_filter_data =
> +                ldr->fdt_filter(opaque, data, match_data, &load_addr);
>       }
>
>       load_addr = ldr->addr_to_phys(opaque, load_addr);
>       sz = fdt_totalsize(load_data);
>       rom_add_blob_fixed(name, load_data, sz, load_addr);
>
> -    ret = 0;
> -out:
> -    g_free((void *) data);
> -    if (data != load_data) {
> -        g_free((void *) load_data);
> -    }
> -    return ret;
> +    return 0;
>   }

Looks like a sensible separate cleanup patch to me.  Care to post it?

Thanks!