Re: [Qemu-devel] [PATCH 25/29] 9pfs: local: symlink: don't follow symlinks

[Stefan Hajnoczi]

On Mon, Feb 20, 2017 at 03:42:34PM +0100, Greg Kurz wrote:
> The local_symlink() callback is vulnerable to symlink attacks because it
> calls:
> 
> (1) symlink() which follows symbolic links for all path elements but the
>     rightmost one
> (2) open(O_NOFOLLOW) which follows symbolic links for all path elements but
>     the rightmost one
> (3) local_set_xattr()->setxattr() which follows symbolic links for all
>     path elements
> (4) local_set_mapped_file_attr() which calls in turn local_fopen() and
>     mkdir(), both functions following symbolic links for all path
>     elements but the rightmost one
> 
> This patch converts local_symlink() to rely on opendir_nofollow() and
> symlinkat() to fix (1), openat(O_NOFOLLOW) to fix (2), as well as
> local_set_xattrat() and local_set_mapped_file_attrat() to fix (3) and
> (4) respectively.
> 
> This partly fixes CVE-2016-9602.
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>  hw/9pfs/9p-local.c |   81 
> ++++++++++++++++------------------------------------
>  1 file changed, 25 insertions(+), 56 deletions(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

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