Zack's Kernel News
Zack's Kernel News
Chronicler Zack Brown reports on the latest news, views, dilemmas, and developments within the Linux kernel community.
Inheriting Filesystem Capabilities
Christoph Lameter posted a patch to make filesystem capabilities inheritable the way the SUID bit is. When you set the SUID bit in an executable and another user runs that executable, it runs with your permissions, rather than the permissions of that user. Any files it creates, or other programs it invokes, are likewise run as you instead of as that user.
Capabilities don't have that kind of inheritability. So, if you write a script and give it certain capabilities, such as allowing raw network access, any scripts invoked by that script will not have the capability to do raw network access. Thus, the script would not be able to rely on any other tools to help do that part of its work. Christoph said, "This is behavior that is counterintuitive to the expected behavior of processes in Unix."
Making capabilities inheritable, Christoph said, was preferable to simply running executables with the SUID bit set. The SUID bit is a very blunt tool, giving the executable *all* the permissions of its owner; whereas capabilities are more surgical, allowing you to constrain those permissions to just the set what is needed.
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