Re: [dm-devel] [PATCH] libmultipath: fix memory leaks in coalesce_paths

[Martin Wilck <mwilck@suse.com>]

On Fri, 2020-10-16 at 14:23 +0800, lixiaokeng wrote:
> When multipath -F are executed firstly and multipath -v2 or
> -d are executed later, asan will warn memory leaks. The
> reason is that the mpp allocated in coalesce_paths isn't
> freed. Here we add newmp in configure(multipath) to store
> mpp and free it.
> 
> Signed-off-by: Lixiaokeng <lixiaokeng@huawei.com>
> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> Signed-off-by: Linfeilong <linfeilong@huawei.com>

Besides what Ben noted already, I think you shouldn't force callers to
pass a non-NULL "newmp". The tricky part is to make sure that paths
aren't handled repeatedly in the CMD_DRY_RUN case. Currently pp->mpp !=
NULL is the condition used by coalesce_paths() to check if a path has
already been dealt with; if you simply call remove_map(), that won't
work any more. I suppose you realized that, and that's why you
introduced the non-NULL newmp in multipath (you should have mentioned
that in the changelog message).

I suggest to have callers pass a "vector *pnewmp" instead of "vector
newmp", always allocate newmp in coalesce_paths(), and upon return,
either free newmp, or assign it to the pointer passed by the caller:

     if (pnewmp)
	    *pnewmp = newmp;
     else
            free_multipathvec(newmp, KEEP_PATHS);

Regards,
Martin


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