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Re: Filenames with trailing newlines wreak havoc

From: Mark J Cox <mark_at_awe.com>
Date: Thu, 18 Apr 2013 19:11:20 +0100

Please use CVE-2013-1968

Mark

On Sun, Apr 14, 2013 at 6:03 PM, Ben Reser <ben_at_reser.org> wrote:
> Apache security folks please provide us a CVE for this.
>
> On Tue, Mar 26, 2013 at 6:36 AM, Stefan Sperling <stsp_at_elego.de> wrote:
>> When a file with a trailing newline (ASCII 0x0a) has made its way into
>> the repository, there are various areas of the system that exhibit failure
>> modes. Failure modes I observed in one particular case are discussed below.
>>
>> I intend to file separate issues for each failure mode to keep track of
>> them, rather than filing one giant issue for them all. Though perhaps
>> a meta-issue that depends on the other issues would be useful.
>>
>> In the case observed there was a file, added in a revision rX, which had
>> a trailing newline in its name. The file was added along with its parent
>> directory (which was also new in rX) and alongside several other files
>> in the same directory which did not have trailing newlines in their names.
>>
>> The server was running Subversion 1.7.8, but might have been running
>> an older release at the time when rX was committed.
>> All commands listed below were run with Subversion 1.7.8.
>>
>> Immediately visible problems were:
>>
>> svnadmin verify resulted in an error for the revision: 'svnadmin: E160013: File not found: ...')
>>
>> svnsync failed to sync the revision ('svnsync: E160013: File not found: ...')
>>
>> However, the directory at rX could be listed (with svn ls) and checked
>> out successfully.
>>
>> During checkout, RA layers were behaving inconsistently.
>>
>> Checkout via ra_svn and ra_local resulted in the expected filename
>> with \n (0x0a) as the last byte both in wc.db (local_relpath NODES
>> column) and on disk.
>>
>> However, ra_neon (didn't try serf) checked the file out with a trailing
>> space (0x20) instead of a trailing newline. The filename was stored with
>> a trailing 0x20 in wc.db as well as on disk.
>>
>> Examining the FSFS revision file [*] of rX showed that the filename was
>> stored with a newline as part of its parent directory's representation.
>>
>> [*] For those who didn't know, the FSFS revision file format is documented
>> here: https://svn.apache.org/repos/asf/subversion/trunk/subversion/libsvn_fs_fs/structure
>>
>> Let's call the parent directory 'A', and the file in question 'alpha\n'.
>> A file named 'alpha\n' added in r1 might appear like this in its parent
>> directory's representation (i.e. the rep of 'A'):
>> ============
>> PLAIN
>> K 6
>> alpha
>>
>> V 17
>> file 2-1.0.r1/122
>> ============
>>
>> However, the cpath: field within the file's own representation did not
>> contain the trailing newline.
>>
>> Also, the file was listed in the changed-paths data section without
>> the trailing newline. Note that the FSFS format docs say "The changed-path
>> data is represented as a series of changed-path items, each consisting of
>> two lines." -- i.e. a trailing newline is considered to be part of revision
>> file data, rather than the filename.
>>
>> Furthermore, several children of the newly-added-in rX 'A' directory
>> were missing from the changed-paths list in the revision file, for an
>> unkown reason.
>> More precisely, children listed after 'alpha\n' in the rep of A were
>> missing from the changed paths list. This was not detected by 'svnadmin
>> verify' (which, in my opinion, is a bug) but was detected by 'svnsync'
>> when a later revision rY referred to one of the missing children in
>> copyfrom information. It turned out that the slave server was missing
>> any children of A not listed in the changed-paths list in the rX
>> revision file on the master server. What kind of consistency checks
>> could prevent this from happening remains to be determined. Perhaps
>> 'svnadmin verify' could cross-check the changed paths list with node-rev
>> IDs which appear in the revision's directory listings?
>>
>> The revision rX could be fixed by removing the trailing newline from the
>> filename in the parent directory's representation, and adjusting the
>> rep's length and checksum information accordingly. About two dozen other
>> revisions had to be adjusted as well because they listed the file
>> 'alpha\n' as part of the 'A' directory rep (which is of course written
>> out in its entirety whenever a revision changes some child of 'A').
>>
>> Also, the changed-paths list of rX had to be extended to add the missing
>> newly added children of A. Other revisions had to be checked for similar
>> omissions in the changed-paths list.
>>
>> How the filename entered the repository is not known with absolute
>> certainty. The current theory, based on discussion with the revision's
>> author, is that the file was checked in using Eclipse with SVNKit 1.6
>> and was not refused by the Subversion server at the time.
>>
>> Attempting the reproduce this problem with a stock Subversion client
>> in a naive way fails because libsvn_client refuses to add such files
>> to version control in the first place:
>>
>> subversion/svn/add-cmd.c:86: (apr_err=160005)
>> subversion/svn/util.c:621: (apr_err=160005)
>> subversion/libsvn_client/add.c:1031: (apr_err=160005)
>> subversion/libsvn_client/add.c:937: (apr_err=160005)
>> subversion/libsvn_client/add.c:320: (apr_err=160005)
>> subversion/libsvn_wc/adm_ops.c:1004: (apr_err=160005)
>> subversion/libsvn_wc/adm_ops.c:679: (apr_err=160005)
>> subversion/libsvn_subr/path.c:1231: (apr_err=160005)
>> svn: E160005: Invalid control character '0x0a' in path '/tmp/wc/alpha\012'
>>
>> This error does not seem to be triggered by our test suite, which
>> is bad because it would have allowed the SVNKit developers to prevent
>> this problem from happening (they use our test suite to test their
>> Java-based implementation of Subversion). There is a tab_test() in
>> commit_tests.py, but that test only tries a tab, not a newline character.
>>
>> We should add some C tests as well to verify API behaviour at the
>> client layer and at the repos layer.
>>
>> Given the ripple effects of this problem in FSFS revision files I think
>> we should ensure that the Subversion server blocks such filenames from
>> entering the repository (any repository, FSFS and BDB). It seems FSFS format
>> changes would be required to support filenames with trailing newlines
>> properly, an effort which isn't worth the gain in my opinion.
>>
>> And given the ripple effects seen in areas such as repository verification,
>> svnsync, and ra_neon, I don't think we can afford to call this a supported
>> use case until all components of the system have been fixed to handle
>> filenames with trailing newlines properly.
>>
>> Comments and opinions are very welcome. I intend to make sure that this
>> problem cannot happen with future Subversion releases, and welcome any
>> input and help I can get.
>
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Received on 2013-04-19 01:36:30 CEST

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