Bug 1312575 - patch (and other utilities) act oddly with respect to custom Linux LSM (i.e., replacing SELinux)
patch (and other utilities) act oddly with respect to custom Linux LSM (i.e.,...
Product: Fedora
Classification: Fedora
Component: patch (Show other bugs)
Unspecified Unspecified
unspecified Severity unspecified
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Assigned To: Tim Waugh
Fedora Extras Quality Assurance
Depends On:
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Reported: 2016-02-27 08:45 EST by W. Michael Petullo
Modified: 2016-12-20 14:04 EST (History)
2 users (show)

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Doc Type: Bug Fix
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Last Closed: 2016-12-20 14:04:09 EST
Type: Bug
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Description W. Michael Petullo 2016-02-27 08:45:21 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):

How reproducible:
Every time

Additional info:
Other utilities exhibit similar behavior. I can address those with additional reports if the patch maintainers decide that this issue warrants attention.
Comment 1 Daniel Walsh 2016-02-29 14:49:13 EST
Michael, what is the security reasons for blocking reading xattr data on files that you own?  Could SELinux be special cased?
Comment 2 W. Michael Petullo 2016-02-29 16:33:37 EST
(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.
Comment 3 Fedora End Of Life 2016-11-24 10:47:55 EST
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Comment 4 Fedora End Of Life 2016-12-20 14:04:09 EST
Fedora 23 changed to end-of-life (EOL) status on 2016-12-20. Fedora 23 is
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