Re: [v3 for-next 1/3] block: Reject unknown status tags in error injection rules

[Mohamed Khalfella <mkhalfella@purestorage.com>]

On Thu 2026-11-05 21:00:27 +0100, Haris Iqbal wrote:
> 
> 
> On 10/21/26 00:34, Mohamed Khalfella wrote:
> > On Mon 2026-10-05 10:49:17 +0200, Christoph Hellwig wrote:
> >> On Tue, Sep 29, 2026 at 12:16:32AM +0200, Md Haris Iqbal wrote:
> >>> tag_to_blk_status() returns BLK_STS_OK both for the "OK" tag and for a
> >>> tag it does not recognize, so a caller cannot tell the two apart. The
> >>> block error injection code (which is the sole user of this function
> >>> currently) relies on error_inject_add() later to reject adding a rule with
> >>> status=BLK_STS_OK. This is okay for the current state of error injection.
> >>>
> >>> The delay option added in the next commit makes the rule with status=OK
> >>> valid, meaning the function tag_to_blk_status() now needs to explicitly
> >>> match BLK_STS_OK for it, and fail for a tag it does not recognize. Hence
> >>> make tag_to_blk_status() take a second param to update the matched status,
> >>> and return true in case of a successful match. If a match is not found,
> >>> the function tag_to_blk_status() returns false and *status remains
> >>> unchanged.
> >>>
> >>> A repeated status= where an invalid tag comes first is now rejected
> >>> instead of being overridden by the later one.
> >>>
> >>> Cc: Christoph Hellwig <hch@lst.de>
> >>> Assisted-by: Claude:claude-opus-5
> >>> Signed-off-by: Md Haris Iqbal <haris.iqbal@linux.dev>
> >>> ---
> >>>   block/blk-core.c        | 14 ++++++--------
> >>>   block/blk.h             |  2 +-
> >>>   block/error-injection.c |  7 ++++---
> >>>   3 files changed, 11 insertions(+), 12 deletions(-)
> >>>
> >>> diff --git a/block/blk-core.c b/block/blk-core.c
> >>> index 13dc70e8f55d..c45846b9c50d 100644
> >>> --- a/block/blk-core.c
> >>> +++ b/block/blk-core.c
> >>> @@ -225,21 +225,19 @@ const char *blk_status_to_tag(blk_status_t status)
> >>>   	return blk_errors[idx].tag;
> >>>   }
> >>>   
> >>> -blk_status_t tag_to_blk_status(const char *tag)
> >>> +bool tag_to_blk_status(const char *tag, blk_status_t *status)
> >>>   {
> >>>   	int i;
> >>>   
> >>>   	for (i = 0; i < ARRAY_SIZE(blk_errors); i++) {
> >>>   		if (blk_errors[i].tag &&
> >>> -		    !strcmp(blk_errors[i].tag, tag))
> >>> -			return (__force blk_status_t)i;
> >>> +		    !strcmp(blk_errors[i].tag, tag)) {
> >>> +			*status = (__force blk_status_t)i;
> >>> +			return true;
> >>> +		}
> >>>   	}
> >>>   
> >>> -	/*
> >>> -	 * Return BLK_STS_OK for mismatches as this function is intended to
> >>> -	 * parse error status values.
> >>> -	 */
> >>> -	return BLK_STS_OK;
> >>> +	return false;
> >>>   }
> >>>   
> >>>   /**
> >>> diff --git a/block/blk.h b/block/blk.h
> >>> index 2cc03aa54c53..5fa54162c686 100644
> >>> --- a/block/blk.h
> >>> +++ b/block/blk.h
> >>> @@ -52,7 +52,7 @@ void blk_free_flush_queue(struct blk_flush_queue *q);
> >>>   
> >>>   const char *blk_status_to_str(blk_status_t status);
> >>>   const char *blk_status_to_tag(blk_status_t status);
> >>> -blk_status_t tag_to_blk_status(const char *tag);
> >>> +bool tag_to_blk_status(const char *tag, blk_status_t *status);
> >>>   enum req_op str_to_blk_op(const char *op);
> >>>   
> >>>   bool __blk_mq_unfreeze_queue(struct request_queue *q, bool force_atomic);
> >>> diff --git a/block/error-injection.c b/block/error-injection.c
> >>> index e14bc4b723ef..db543fe27630 100644
> >>> --- a/block/error-injection.c
> >>> +++ b/block/error-injection.c
> >>> @@ -171,15 +171,16 @@ static int match_op(substring_t *args, enum req_op *op)
> >>>   static int match_status(substring_t *args, blk_status_t *status)
> >>>   {
> >>>   	const char *tag;
> >>> +	bool found;
> >>>   
> >>>   	tag = match_strdup(args);
> >>>   	if (!tag)
> >>>   		return -ENOMEM;
> >>> -	*status = tag_to_blk_status(tag);
> >>> -	if (!*status)
> >>> +	found = tag_to_blk_status(tag, status);
> >>> +	if (!found)
> >>>   		pr_warn("invalid status '%s'\n", tag);
> >>>   	kfree(tag);
> >>> -	return 0;
> >>> +	return found ? 0 : -EINVAL;
> >>
> >> 	if (!found) {
> >>    		pr_warn("invalid status '%s'\n", tag);
> >> 		return -EINVAL;
> >> 	}
> >> 	return 0;
> 
> As Mohamed mentioned below, "tag" would leak then.
> 
> > 
> > Doing it this way will result in use-after-free. "tag" has already been
> > freed above.
> > 
> > Maybe change tag_to_blk_status() to return an int (0 on success and
> > -EINVAL on failure) and use its return value without mapping it?
> 
> I am not sure I get your suggestion completely. Even if we change the 
> return type of tag_to_blk_status(), we would have to free the "tag" 
> before returning.

Changing tag_to_blk_status() to return an int will not have an effect or
"tag" like you mentioned. But you will not need to map the return from
that function.

return found ? 0 : -EINVAL;

The line above just returns what tag_to_blk_status() returned.

> 
> What can make it simpler is allocating "tag" on stack, and then use 
> match_strlcpy() instead of match_strdup().

That can work too. Just make sure we limit the string size somehow.