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Re: [Qemu-devel] [PATCH 26/29] 9pfs: local: mknod: don't follow symlinks
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 26/29] 9pfs: local: mknod: don't follow symlinks |
Date: |
Thu, 23 Feb 2017 15:16:17 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Mon, Feb 20, 2017 at 03:42:42PM +0100, Greg Kurz wrote:
> The local_mknod() callback is vulnerable to symlink attacks because it
> calls:
>
> (1) mknod() which follows symbolic links for all path elements but the
> rightmost one
> (2) local_set_xattr()->setxattr() which follows symbolic links for all
> path elements
> (3) 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
> (4) local_post_create_passthrough() which calls in turn lchown() and
> chmod(), both functions also following symbolic links
>
> This patch converts local_mknod() to rely on opendir_nofollow() and
> mknodat() to fix (1), as well as local_set_xattrat() and
> local_set_mapped_file_attrat() to fix (2) and (3) respectively.
>
> A new local_set_cred_passthrough() helper based on fchownat() and fchmod()
> is introduced as a replacement to local_post_create_passthrough() to fix (4).
> No effort is made to factor out code because local_post_create_passthrough()
> will be dropped when all users have been converted to call the new helper.
>
> The mapped and mapped-file security modes are supposed to be identical,
> except for the place where credentials and file modes are stored. While
> here, we also make that explicit by sharing the call to mknodat().
>
> This partly fixes CVE-2016-9602.
>
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> hw/9pfs/9p-local.c | 82
> +++++++++++++++++++++++++++++++---------------------
> 1 file changed, 49 insertions(+), 33 deletions(-)
Reviewed-by: Stefan Hajnoczi <address@hidden>
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- Re: [Qemu-devel] [PATCH 21/29] 9pfs: local: improve error handling in link op, (continued)
- [Qemu-devel] [PATCH 22/29] 9pfs: local: link: don't follow symlinks, Greg Kurz, 2017/02/20
- [Qemu-devel] [PATCH 23/29] 9pfs: local: chmod: don't follow symlinks, Greg Kurz, 2017/02/20
- [Qemu-devel] [PATCH 24/29] 9pfs: local: chown: don't follow symlinks, Greg Kurz, 2017/02/20
- [Qemu-devel] [PATCH 25/29] 9pfs: local: symlink: don't follow symlinks, Greg Kurz, 2017/02/20
- [Qemu-devel] [PATCH 26/29] 9pfs: local: mknod: don't follow symlinks, Greg Kurz, 2017/02/20
- Re: [Qemu-devel] [PATCH 26/29] 9pfs: local: mknod: don't follow symlinks,
Stefan Hajnoczi <=
- [Qemu-devel] [PATCH 27/29] 9pfs: local: mkdir: don't follow symlinks, Greg Kurz, 2017/02/20
- [Qemu-devel] [PATCH 28/29] 9pfs: local: open2: don't follow symlinks, Greg Kurz, 2017/02/20
- [Qemu-devel] [PATCH 29/29] 9pfs: local: drop unused code, Greg Kurz, 2017/02/20