Re: [Exist-development] [HEADS-UP] Merge in of Security Branch

[Hungerburg <pc...@my...>]

Am 2012-02-08 23:03, schrieb Adam Retter:
>
> I just wrote a small bash script and a C program on my Macbook and
> compared the Unix permissions required to execute each, to check.
> The bash script requires both read and execute bits when executed as
> '$ ./hello.sh' and bash cmd requires execute, BUT only requires read
> when executed as '$ bash hello.sh', whilst bash cmd requires execute.
> The C program, only requires the execute bit to execute.

May I explore the unix model? I do not know every detail and simplify a 
lot...

First there is the shell, it wraps the kernel, you use it to operate the 
computer. If you enter "ls" at the prompt, it will interpret this as a 
command and will search PATH for a file, that is called "ls". It will 
then find "/bin/ls", and if this is marked executable it will call to 
the kernel to execute that. The kernel I suppose now has to find out, 
what kind of contents there are in the file. It will have to read the 
first N bytes or the first line and do its magic. If the signature 
matches a process image, it will call the linker to complete it, change 
its persona to the users and hand over execution to it. If the file 
starts with a hashbang #! the kernel will read the name of the 
interpreter from the line, execute that one passing the file name as an 
argument. While the script is running, you will see in "ps" the 
interpreter and the script name. So "./hello.sh" is just a convenient 
shorthand for "/bin/sh hello.sh". One will understand, why a user can 
only run scripts, that she can read.

Only recently, there was this local exploit on linux kernels, where the 
attacker would read some suid binary to determine return addresses of 
functions in order to overwrite them with shell code. Making the command 
NOT readable by the user proved insufficient to prevent the exploit, see 
http://blog.zx2c4.com/749 Update 3.

In eXist speak, the request servlet would map to the shell, the xquery 
servlet to the interpreter. A very clear analogy. Java'd be the native 
executable format. Is it like that? If so, it should not be lightly broken.

-- 
peter