Re: [Qemu-devel] [PATCH v2 10/28] 9pfs: local: lremovexattr: don't follow symlinks

[Stefan Hajnoczi]

On Sun, Feb 26, 2017 at 11:42:51PM +0100, Greg Kurz wrote:
> The local_lremovexattr() callback is vulnerable to symlink attacks because
> it calls lremovexattr() which follows symbolic links in all path elements
> but the rightmost one.
> 
> This patch introduces a helper to emulate the non-existing fremovexattrat()
> function: it is implemented with /proc/self/fd which provides a trusted
> path that can be safely passed to lremovexattr().
> 
> local_lremovexattr() is converted to use this helper and opendir_nofollow().
> 
> This partly fixes CVE-2016-9602.
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> v2: - introduce /proc based fremovexattrat_nofollow()
>     - fix arguments passed to local_removexattr_nofollow()
> ---
>  hw/9pfs/9p-posix-acl.c  |   10 ++--------
>  hw/9pfs/9p-xattr-user.c |    8 +-------
>  hw/9pfs/9p-xattr.c      |   36 +++++++++++++++++++++++++++++++-----
>  hw/9pfs/9p-xattr.h      |    2 ++
>  4 files changed, 36 insertions(+), 20 deletions(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

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