Re: [PATCHv3] Fix range checks in kernfs_get_target_path

[Bernd Edlinger]

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@xxxxxxxxxx>
> ---
>  Âfs/kernfs/symlink.c | 5 ++++-
>  Â1 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
>  ÂÂÂÂÂÂÂÂ if (base == kn)
>  ÂÂÂÂÂÂÂÂÂÂÂÂ break;
> 
> +ÂÂÂÂÂÂÂ if ((s - path) + 3 >= PATH_MAX)
> +ÂÂÂÂÂÂÂÂÂÂÂ return -ENAMETOOLONG;
> +
>  ÂÂÂÂÂÂÂÂ strcpy(s, "../");
>  ÂÂÂÂÂÂÂÂ s += 3;
>  ÂÂÂÂÂÂÂÂ base = base->parent;
> @@ -79,7 +82,7 @@ static int kernfs_get_target_path(struct kernfs_node
>  ÂÂÂÂ if (len < 2)
>  ÂÂÂÂÂÂÂÂ return -EINVAL;
>  ÂÂÂÂ len--;
> -ÂÂÂ if ((s - path) + len > PATH_MAX)
> +ÂÂÂ if ((s - path) + len >= PATH_MAX)
>  ÂÂÂÂÂÂÂÂ return -ENAMETOOLONG;
> 
>  ÂÂÂÂ /* reverse fillup of target string from target to base */