| Message ID | 1470223689-17783-6-git-send-email-jack@suse.cz (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Aug 03, 2016 at 01:28:09PM +0200, Jan Kara wrote: > Currently, notify_change() clears capabilities or IMA attributes by > calling security_inode_killpriv() before calling into ->setattr. Thus it > happens before any other permission checks in inode_change_ok() and user > is thus allowed to trigger clearing of capabilities or IMA attributes > for any file he can look up e.g. by calling chown for that file. This is > unexpected and can lead to user DoSing a system. > > Fix the problem by calling security_inode_killpriv() at the end of > inode_change_ok() instead of from notify_change(). At that moment we are > sure user has permissions to do the requested change. Looks fine, Reviewed-by: Christoph Hellwig <hch@lst.de> -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/attr.c b/fs/attr.c index 5c45909ea204..83c8430d908f 100644 --- a/fs/attr.c +++ b/fs/attr.c @@ -47,7 +47,7 @@ int setattr_prepare(struct dentry *dentry, struct iattr *attr) /* If force is set do it anyway. */ if (ia_valid & ATTR_FORCE) - return 0; + goto kill_priv; /* Make sure a caller can chown. */ if ((ia_valid & ATTR_UID) && @@ -80,6 +80,16 @@ int setattr_prepare(struct dentry *dentry, struct iattr *attr) return -EPERM; } +kill_priv: + /* User has permission for the change */ + if (ia_valid & ATTR_KILL_PRIV) { + int error; + + error = security_inode_killpriv(dentry); + if (error) + return error; + } + return 0; } EXPORT_SYMBOL(setattr_prepare); @@ -220,13 +230,11 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de if (!(ia_valid & ATTR_MTIME_SET)) attr->ia_mtime = now; if (ia_valid & ATTR_KILL_PRIV) { - attr->ia_valid &= ~ATTR_KILL_PRIV; - ia_valid &= ~ATTR_KILL_PRIV; error = security_inode_need_killpriv(dentry); - if (error > 0) - error = security_inode_killpriv(dentry); - if (error) + if (error < 0) return error; + if (error == 0) + ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV; } /*
Currently, notify_change() clears capabilities or IMA attributes by calling security_inode_killpriv() before calling into ->setattr. Thus it happens before any other permission checks in inode_change_ok() and user is thus allowed to trigger clearing of capabilities or IMA attributes for any file he can look up e.g. by calling chown for that file. This is unexpected and can lead to user DoSing a system. Fix the problem by calling security_inode_killpriv() at the end of inode_change_ok() instead of from notify_change(). At that moment we are sure user has permissions to do the requested change. References: CVE-2015-1350 Signed-off-by: Jan Kara <jack@suse.cz> --- fs/attr.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-)