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Date: Mon, 29 Apr 2002 01:11:23 -0700 (PDT)
From: Peter Edwards <pmedwards@eircom.net>
To: freebsd-gnats-submit@FreeBSD.org
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Subject: kern/37554: [PATCH] Make ELF shared libraries immutable once loaded (like executables)
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>Number:         37554
>Category:       kern
>Synopsis:       [PATCH] Make ELF shared libraries immutable once loaded (like executables)
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Mon Apr 29 01:20:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Peter Edwards
>Release:        4-STABLE
>Organization:
>Environment:
FreeBSD rocklobster 4.5-STABLE FreeBSD 4.5-STABLE #30: Mon Apr 29 08:00:03 IST 2002     petere@rocklobster:/pub/FreeBSD/work/src/sys/compile/ROCKLOBSTER  i386

>Description:
Before executing a program, the kernel marks the executable file as
immutable by setting the VTEXT flag in its vnode. This makes write
operations return with ETXTBSY when attempted.

However, no such flag is set for shared libraries mapped by rtld.

This patch adds a new fcntl command, F_TXTBSY, which sets the VTEXT flag
in the vnode associated with the file, and gets rtld-elf to make use
of it.

There may be security issues here, allowing user code to set this flag
in contexts it wasn't designed for, but I don't think it allows you do
anything that you couldn't already. You can't stop someone creating a
custom executable in order to get VTEXT set on it anyway, and root can
always kill any processes holding the object in memory to clear the
flag if neccessary.

>How-To-Repeat:
Write a program that depends on a shared library, and overwrite that
library while the program is running. Bad Things happen.

Trying the same on an executable results in the write operation
returning ETXTBSY
>Fix:
Apply the following patch.

begin 644 shlib-textbusy.tar.Z
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`
end

>Release-Note:
>Audit-Trail:
>Unformatted:

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