Red Hat Bugzilla – Bug 1312575
patch (and other utilities) act oddly with respect to custom Linux LSM (i.e., replacing SELinux)
Last modified: 2016-12-20 14:04:09 EST
Description of problem:
I am working on a custom Linux security module. My module returns -EPERM when a non-root user-space process attempts to invoke getxattr on an extended attribute in the security domain (i.e., name is "security.[something]"). This is different than SELinux which allows non-root user-space processes to view but not update such security attributes.
I have noticed that at least patch and ls do not respond well to this. I realize that my LSM module exhibits non-standard behavior, but I would argue it is not unreasonable behavior. For example running patch causes this to happen:
$ patch -p1 < patch1
can't find file to patch at input line 3
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
This seems to be the result of the lgetxattr library call returning -EPERM, but clearly the error message is deceiving. I think patch ought to print that it cannot maintain the security attribute on the new file. Such an issue might be an error or a warning.
Version-Release number of selected component (if applicable):
Other utilities exhibit similar behavior. I can address those with additional reports if the patch maintainers decide that this issue warrants attention.
Michael, what is the security reasons for blocking reading xattr data on files that you own? Could SELinux be special cased?
(In reply to Daniel Walsh from comment #1)
> Michael, what is the security reasons for blocking reading xattr data on
> files that you own? Could SELinux be special cased?
We are writing a LSM which investigates an alternative security model. Thus we came across this while doing academic research. Our's is clearly not a normal use case, but I thought it might be worthwhile to point out that patch's error handling could be a little more clear and perhaps handle more possible error conditions.
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