linux-kernel - Re: [PATCHv3] Fix range checks in kernfs_get_target

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Message-ID: <AM5PR0701MB265723084A8E48954B914CF4E4340@AM5PR0701MB2657.eurprd07.prod.outlook.com>
Date:   Sun, 26 Aug 2018 10:55:24 +0000
From:   Bernd Edlinger <bernd.edlinger@...mail.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv3] Fix range checks in kernfs_get_target_path

Ping...
Sorry, I had actually completely forgotten about this one.

On 07/07/18 19:52, Bernd Edlinger wrote:
> The terminating NUL byte is only there because the buffer is
> allocated with kzalloc(PAGE_SIZE, GFP_KERNEL), but since the
> range-check is off-by-one, and PAGE_SIZE==PATH_MAX, the
> returned string may not be zero-terminated if it is exactly
> PATH_MAX characters long.  Furthermore also the initial loop
> may theoretically exceed PATH_MAX and cause a fault.
> 
> Signed-off-by: Bernd Edlinger <bernd.edlinger@...mail.de>
> ---
>   fs/kernfs/symlink.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c
> index 08ccabd..774bada 100644
> --- a/fs/kernfs/symlink.c
> +++ b/fs/kernfs/symlink.c
> @@ -63,6 +63,9 @@ static int kernfs_get_target_path(struct kernfs_node
>           if (base == kn)
>               break;
> 
> +        if ((s - path) + 3 >= PATH_MAX)
> +            return -ENAMETOOLONG;
> +
>           strcpy(s, "../");
>           s += 3;
>           base = base->parent;
> @@ -79,7 +82,7 @@ static int kernfs_get_target_path(struct kernfs_node
>       if (len < 2)
>           return -EINVAL;
>       len--;
> -    if ((s - path) + len > PATH_MAX)
> +    if ((s - path) + len >= PATH_MAX)
>           return -ENAMETOOLONG;
> 
>       /* reverse fillup of target string from target to base */