issue with unsetting 'arch' flag
Garrett Cooper
gcooper at FreeBSD.org
Thu Oct 7 05:38:12 UTC 2010
On Wed, Oct 6, 2010 at 4:03 PM, Garrett Cooper <gcooper at freebsd.org> wrote:
> On Wed, Oct 6, 2010 at 3:01 PM, Sergey Kandaurov <pluknet at gmail.com> wrote:
>> On 6 October 2010 23:38, Alexander Best <arundel at freebsd.org> wrote:
>>> On Wed Oct 6 10, Garrett Cooper wrote:
>>>> On Wed, Oct 6, 2010 at 10:35 AM, Alexander Best <arundel at freebsd.org> wrote:
>>>> > On Wed Oct 6 10, Garrett Cooper wrote:
>>>> >> On Tue, Oct 5, 2010 at 4:50 PM, Alexander Best <arundel at freebsd.org> wrote:
>>>> >> > hi there,
>>>> >> >
>>>> >> > i think the following example shows the problem better than a long explanation:
>>>> >> >
>>>> >> > `touch ftest && chflags arch ftest && chflags -vv 0 ftest`.
>>>> >> > ^^non-root ^^root ^^non-root
>>>> >> >
>>>> >> > chflags claims to have cleared the 'arch' flag (which should be impossible as
>>>> >> > non-root user), but indeed has done nothing.
>>>> >> >
>>>> >> > i've tried the same with 'sappnd' and that works as can be expected.
>>>> >> >
>>>> >> > The issue was confirmed to exist in HEAD (me), stable/8 (pgollucc1, jpaetzel)
>>>> >> > and stable/7 (nox).
>>>> >> > On stable/6 it does NOT exist (jpaetzel). chflags properly fails with EPERM.
>>>> >>
>>>> >> Fails for me when I call the syscall directly, as I would expect,
>>>> >> and passes when I'm superuser:
>>>> >>
>>>> >> $ ./test_chflags
>>>> >> (uid, euid) = (1000, 1000)
>>>> >> test_chflags: chflags: Operation not permitted
>>>> >> test_chflags: lchflags: Operation not permitted
>>>> >> $ sudo ./test_chflags
>>>> >> (uid, euid) = (0, 0)
>>>> >>
>>>> >> According to my basic inspection in strtofflags
>>>> >> (.../lib/libc/gen/strtofflags.c), it works as well.
>>>> >> And last but not least, executing the commands directly on the CLI work:
>>>> >>
>>>> >> $ tmpfile=`mktemp /tmp/chflags.XXXXXX`
>>>> >> $ chflags arch $tmpfile
>>>> >> chflags: /tmp/chflags.nQm1IL: Operation not permitted
>>>> >> $ rm $tmpfile
>>>> >> $ tmpfile=`mktemp /tmp/chflags.XXXXXX`
>>>> >> $ sudo chflags arch $tmpfile
>>>> >> $ sudo chflags noarch $tmpfile
>>>> >> $ rm $tmpfile
>>>> >
>>>> > thanks for your test app and helping out with this problem. i'm not sure
>>>> > however you understood the problem. probably i didn't explain it right:
>>>> >
>>>> > $ sudo rm -d /tmp/chflags.XXXXXX
>>>> > $ tmpfile=`mktemp /tmp/chflags.XXXXXX`
>>>> > $ sudo chflags arch $tmpfile
>>>> > $ chflags noarch $tmpfile
>>>> >
>>>> > is what's causing the problem. the last chflags call should fail, but it
>>>> > doesn't.
>>>>
>>>> Sorry... my CLI based example was stupid. I meant:
>>>>
>>>> $ tmpfile=`mktemp /tmp/chflags.XXXXXX`
>>>> $ chflags arch $tmpfile
>>>> chflags: /tmp/chflags.V2NpXR: Operation not permitted
>>>> $ chflags noarch $tmpfile
>>>> $ rm $tmpfile
>>>>
>>>> Currently chflags(2) states:
>>>>
>>>> The SF_IMMUTABLE, SF_APPEND, SF_NOUNLINK, and SF_ARCHIVED flags may only
>>>> be set or unset by the super-user. Attempts to set these flags by non-
>>>> super-users are rejected, >>> attempts by non-superusers to clear
>>>> flags that
>>>> are already unset are silently ignored. <<< These flags may be set at any
>>>> time, but normally may only be unset when the system is in single-user
>>>> mode. (See init(8) for details.)
>>>>
>>>> So this behavior is already well documented :). The EPERM section
>>>> should really note SF_ARCHIVED though (whoever added the flag forgot
>>>> to add that particular item to the ERRORS section).
>>>
>>> that's perfectly alright. clearing an unset flag shouldn't cause any error to
>>> be returned. however in my example arch *does* get set and still trying to
>>> unset it as normal user doesn't return an error.
>>>
>>
>> It's even more interesting.
>>
>> As far as I could parse the code:
>> - UFS has no special handling for SF_ARCHIVED (I found only it for msdosfs)
>
> _very_ interesting:
>
> [/sys]$ grep -r SF_ARCHIVED kern/ fs/ ufs/ | grep -v svn
> fs/msdosfs/msdosfs_vnops.c: vap->va_flags |= SF_ARCHIVED;
> fs/msdosfs/msdosfs_vnops.c: if (vap->va_flags & ~SF_ARCHIVED)
> fs/msdosfs/msdosfs_vnops.c: if (vap->va_flags & SF_ARCHIVED)
>
> The commit that introduced this change probably wasn't doing the
> right thing: http://svn.freebsd.org/viewvc/base/head/sys/fs/msdosfs/msdosfs_vnops.c?revision=5241&view=markup
> ; cp(1) probably should have been fixed in lieu of `fixing' msdosfs.
>
>> - ufs_setattr() does not handle unsetting SF_ARCHIVED,
>> so all what it does is simply return zero.
>
> [EOPNOTSUPP] The underlying file system does not support file
> flags.
>
> So I would expect for invalid flags to return EOPNOTSUPP.
>
> ...
>
> $ ~/test_chflags_negative
> test_chflags_negative: should not get here
> $ sudo ~/test_chflags_negative
> test_chflags_negative: should not get here
>
> *facepalm*
>
> I think the problem in part is here (sys/stat.h):
>
> *
> * Super-user and owner changeable flags.
> */
> #define UF_SETTABLE 0x0000ffff /* mask of owner changeable flags */
> #define UF_NODUMP 0x00000001 /* do not dump file */
> #define UF_IMMUTABLE 0x00000002 /* file may not be changed */
> #define UF_APPEND 0x00000004 /* writes to file may only append */
> #define UF_OPAQUE 0x00000008 /* directory is opaque wrt. union */
> #define UF_NOUNLINK 0x00000010 /* file may not be removed or renamed */
> /*
> * Super-user changeable flags.
> */
> #define SF_SETTABLE 0xffff0000 /* mask of superuser changeable flags */
> #define SF_ARCHIVED 0x00010000 /* file is archived */
> #define SF_IMMUTABLE 0x00020000 /* file may not be changed */
> #define SF_APPEND 0x00040000 /* writes to file may only append */
> #define SF_NOUNLINK 0x00100000 /* file may not be removed or renamed */
> #define SF_SNAPSHOT 0x00200000 /* snapshot inode */
>
> Note the *_SETTABLE macros, and the fact that they allow for more
> functionality than what's currently slotted with the one-hot encoded
> flags currently available.
> SF_ARCHIVED is not present in the other BSDs or Mac OSX either (I
> did some hunting for a python bug related to chflags a few weeks
> ago)... and I'm not even sure what this functionality really buys us
> because it's not well described (but I'd be happy to get an
> explanation/history lesson).
>
>> - /bin/chflags doesn't check the actual flags value from inode after
>> calling chflags() syscall, and blindly assumes all is well, if chflags()
>> returns with zero,
>
> Yeah... but ideally tests should be written for this stuff and
> exercised on all filesystems and exercised whenever code in this
> particular path is changed, because that would potentially turn into a
> noticeable performance hit [depending on how it's implemented in
> chflags(1)]. And lo and behold it already does exist under
> .../tools/regression/fstest/tests/chflags . I'll audit this once I get
> back home...
For starters, the tests were moved to .../tools/regression/pjdfstest .
This fixes the manpage and the negative flags testcase at least. I
ran the pjdfstest on a UFS2 partition on my test machine and tmpfs,
and it passed chflags with flying colors. msdosfs unfortunately isn't
supported yet, but I did some manual testing and everything seemed ok.
I also need to check and see whether or not pjdfstest is doing the
right job with negative testcases.
I didn't have a ext2/3 or zfs pool to test with, so if someone
could poke around with those filesystems it would be much appreciated
:).
And finally, here are all of the references in the sourcebase to
SF_ARCHIVED:
# /usr/local/bin/svnversion
213377M
# grep -r SF_ARCHIVED /usr/src/ | grep -v svn
grep: /usr/src/tools/regression/pjdfstest/pjdfstest_5aaec5b222b60945b16daa0e8d61313d/pjdfstest_b4353ca81458e0bfc9ec5be8ff741eb2/usr/src/tools/regression/priv/priv_vfs_chflags.c: flags
|= SF_ARCHIVED;
/usr/src/tools/regression/priv/priv_vfs_chflags.c: flags |= SF_ARCHIVED;
/usr/src/tools/regression/priv/priv_vfs_chflags.c: flags |= SF_ARCHIVED;
/usr/src/tools/regression/pjdfstest/tests/chflags/00.t: allflags="UF_NODUMP,UF_IMMUTABLE,UF_APPEND,UF_NOUNLINK,UF_OPAQUE,SF_ARCHIVED,SF_IMMUTABLE,SF_APPEND,SF_NOUNLINK"
/usr/src/tools/regression/pjdfstest/tests/chflags/00.t: systemflags="SF_ARCHIVED,SF_IMMUTABLE,SF_APPEND,SF_NOUNLINK"
Binary file /usr/src/tools/regression/pjdfstest/pjdfstest matches
/usr/src/tools/regression/pjdfstest/pjdfstest.c:#ifdef SF_ARCHIVED
/usr/src/tools/regression/pjdfstest/pjdfstest.c: { SF_ARCHIVED, "SF_ARCHIVED" },
: Operation not supported
grep: warning: /usr/src/sys/modules/tmpfs/@: recursive directory loop
/usr/src/lib/libc/gen/strtofflags.c: { "noarch", SF_ARCHIVED, 0 },
/usr/src/lib/libc/gen/strtofflags.c: { "noarchived", SF_ARCHIVED, 0 },
/usr/src/lib/libc/sys/chflags.2:.It Dv SF_ARCHIVED
/usr/src/lib/libc/sys/chflags.2:.Dv SF_ARCHIVED
/usr/src/lib/libc/sys/chflags.2:.Dv SF_ARCHIVED , SF_IMMUTABLE , SF_APPEND ,
/usr/src/lib/libc/sys/chflags.2:.Dv SF_ARCHIVED , SF_IMMUTABLE , SF_APPEND ,
/usr/src/lib/libarchive/archive_entry.c:#ifdef SF_ARCHIVED
/usr/src/lib/libarchive/archive_entry.c: {
"noarch", L"noarch", SF_ARCHIVED, 0 },
/usr/src/lib/libarchive/archive_entry.c: {
"noarchived", L"noarchived", SF_ARCHIVED, 0 },
/usr/src/sys/fs/msdosfs/msdosfs_vnops.c: vap->va_flags |= SF_ARCHIVED;
/usr/src/sys/fs/msdosfs/msdosfs_vnops.c: if (vap->va_flags & ~SF_ARCHIVED)
/usr/src/sys/fs/msdosfs/msdosfs_vnops.c: if (vap->va_flags & SF_ARCHIVED)
/usr/src/sys/sys/stat.h:#define SF_ARCHIVED 0x00010000 /* file is archived */
/usr/src/sys/sys/stat.h:#define SF_SETTABLE (SF_ARCHIVED |
SF_IMMUTABLE | SF_APPEND | \
So it doesn't look like anything's utilizing the functionality,
other than msdosfs, and all that really does is tweak the following
attribute:
#define ATTR_ARCHIVE 0x20 /* file is new or modified */
and vice versa. I vaguely remember archive file types in FAT32
from the Win95 days, but my memory is a bit hazy as to what the
attribute actually does.
Thanks,
-Garrett
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