On Sun, Feb 26, 2017 at 11:44:54PM +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 > fchmodat_nofollow() is introduced as a replacement to > local_post_create_passthrough() to fix (4). > > 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 <gr...@kaod.org> > --- > v2: - use fchmodat_nofollow() > --- > hw/9pfs/9p-local.c | 68 > +++++++++++++++++++++++++++------------------------- > 1 file changed, 35 insertions(+), 33 deletions(-)
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
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