[Bug 194695] New: size overflow detected in function ext4_mb_new_group_pa

[Bug 194695] New: size overflow detected in function ext4_mb_new_group_pa

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=194695

            Bug ID: 194695
           Summary: size overflow detected in function
                    ext4_mb_new_group_pa
           Product: File System
           Version: 2.5
    Kernel Version: 4.9.10-1+grsec201702162016+1
          Hardware: x86-64
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ext4
          Assignee: fs_ext4@kernel-bugs.osdl.org
          Reporter: matthijs@cacholong.nl
        Regression: No

I am trying to run a kernel with grsecurity with the size overflow
protection and am getting the following warnings / errors:

dmesg: http://pastebin.com/wr3UGLS9
config: http://pastebin.com/sr8M9bP0
mballoc.* (make fs/ext4/mballoc.o EXTRA_CFLAGS="-fdump-tree-all
-fdump-ipa-all") http://filebin.ca/3DMIChVw9lQM/mballoc.tgz

According to the grsecurity developers it seems to be a bug in ext4, see for
some background here:
https://forums.grsecurity.net/viewtopic.php?f=1&t=4678&p=16971

The response from ephox (PAX team / grsecurity developer):
--
Thanks for the report. I think this is an upstream bug. Based on the
runtime values provided by you, ext4_mb_new_group_pa() tries to store a
value into pa->pa_lstart which larger than UINT_MAX which comes from
ext4_group_first_block_no().
Could you please report it to the ext4 developers?
--

I'll try to answer all the questions but I'm not an expert in this area.

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[Bug 194695] size overflow detected in function ext4_mb_new_group_pa

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=194695

Andreas Dilger (adilger.kernelbugzilla@dilger.ca) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |adilger.kernelbugzilla@dilg
                   |                            |er.ca

--- Comment #1 from Andreas Dilger (adilger.kernelbugzilla@dilger.ca) ---
Definitely looks like a real bug in:

        pa->pa_pstart = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
        pa->pa_lstart = pa->pa_pstart;

pa_pstart is 64-bit, pa_lstart is 32-bit.

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[Bug 194695] size overflow detected in function ext4_mb_new_group_pa

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=194695

Theodore Tso (tytso@mit.edu) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tytso@mit.edu

--- Comment #2 from Theodore Tso (tytso@mit.edu) ---
I don't think we use the pa_lstart value for group preallocations --- a logical
number doesn't really have meaning for group pa's.  That being said, the
preallocation code is really quite a mess, and it makes it hard to follow.   We
should really look at cleaning it up....

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