linux-kernel - Re: [PATCH] cifs: check pointer before freeing

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Date:   Tue, 5 Jan 2021 15:25:59 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     trix@...hat.com
Cc:     sfrench@...ba.org, ndesaulniers@...gle.com, aaptel@...e.com,
        palcantara@...e.de, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] cifs: check pointer before freeing

On Tue, Jan 05, 2021 at 12:21:26PM -0800, trix@...hat.com wrote:
> From: Tom Rix <trix@...hat.com>
> 
> clang static analysis reports this problem
> 
> dfs_cache.c:591:2: warning: Argument to kfree() is a constant address
>   (18446744073709551614), which is not memory allocated by malloc()
>         kfree(vi);
>         ^~~~~~~~~
> 
> In dfs_cache_del_vol() the volume info pointer 'vi' being freed
> is the return of a call to find_vol().  The large constant address
> is find_vol() returning an error.
> 
> Add an error check to dfs_cache_del_vol() similar to the one done
> in dfs_cache_update_vol().
> 
> Fixes: 54be1f6c1c37 ("cifs: Add DFS cache routines")
> Signed-off-by: Tom Rix <trix@...hat.com>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

> ---
>  fs/cifs/dfs_cache.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c
> index 6ad6ba5f6ebe..0fdb0de7ff86 100644
> --- a/fs/cifs/dfs_cache.c
> +++ b/fs/cifs/dfs_cache.c
> @@ -1260,7 +1260,8 @@ void dfs_cache_del_vol(const char *fullpath)
>  	vi = find_vol(fullpath);
>  	spin_unlock(&vol_list_lock);
>  
> -	kref_put(&vi->refcnt, vol_release);
> +	if (!IS_ERR(vi))
> +		kref_put(&vi->refcnt, vol_release);
>  }
>  
>  /**
> -- 
> 2.27.0
>