On Thu, Jan 09, 2020 at 02:46:41PM -0800, Emily Shaffer wrote:
> > Perhaps. The integrity check only protects against an index that was
> > modified after the fact, not one that was generated by a buggy Git. I'm
> > not sure we know how the index that led to this patch got into this
> > state (though it sounds like Emily has a copy and could check the hash
> > on it), but other cache-tree segfault I found recently was with an index
> > with an intact integrity hash.
>
> Yeah, I can do that, although I'm not sure how. The index itself is very
> small - it only contains one file and one tree extension - so I'll go
> ahead and paste some poking and prodding, and if it's not what you
> wanted then please let me know what else to run.
I was thinking you would run something like:
size=$(stat --format=%s "$file")
actual=$(head -c $(($size-20)) "$file" | sha1sum | awk '{print $1}')
expect=$(xxd -s -20 -g 20 -c 20 "$file" | awk '{print $2}')
if test "$actual" = "$expect"; then
echo "OK ($actual)"
else
echo "FAIL ($actual != $expect)"
fi
to manually check the sha1. But...
> $ g fsck --cache
> Checking object directories: 100% (256/256), done.
> Checking objects: 100% (20/20), done.
> broken link from commit 153a9a100eae7fdba5989ce39a5dd1782075517f
> to commit cca7ecaa5d8c398f41bfec7938cc6a526803579b
> broken link from commit 7d6bb91e31d18eadfaf855a9fb7ad6ba81b8b6d9
> to commit 03087a617bfe55f862cb1ef43273a2bd08e8b6d6
> missing commit 03087a617bfe55f862cb1ef43273a2bd08e8b6d6
> missing commit cca7ecaa5d8c398f41bfec7938cc6a526803579b
> dangling commit 5e2c635433bc46b13061b276e481f63b1f6642c8
...fsck would have reported a problem there, since we explicitly kept
the check there in a33fc72fe9 (read-cache: force_verify_index_checksum,
2017-04-14).
And just to be double-sure, I used this:
> $ hexdump -C .git/index
> 00000000 44 49 52 43 00 00 00 02 00 00 00 01 5d 89 5e 22 |DIRC........].^"|
> 00000010 23 bf a3 c4 5d 89 5e 22 23 bf a3 c4 00 00 fe 02 |#...].^"#.......|
> 00000020 02 c8 f5 83 00 00 81 a4 00 06 c1 dc 00 01 5f 53 |.............._S|
> 00000030 00 00 06 b3 78 88 a4 f4 22 34 7d ad b0 c4 73 0f |....x..."4}...s.|
> 00000040 c5 bc f6 ea 1d 2d f0 3a 00 09 52 45 41 44 4d 45 |.....-.:..README|
> 00000050 2e 6d 64 00 54 52 45 45 00 00 00 3a 00 31 37 20 |.md.TREE...:.17 |
> 00000060 31 0a da 7f 67 25 40 7d 4e ce 9f d3 72 ce 4c e8 |1...g%@}N...r.L.|
> 00000070 40 6d 5d ad e9 79 67 69 74 6c 69 6e 74 00 34 20 |@m]..ygitlint.4 |
> 00000080 30 0a 93 63 25 17 69 e6 d6 92 78 97 55 4b 0f 8b |0..c%.i...x.UK..|
> 00000090 ff a0 e8 2d 6d 71 32 d1 69 fc f2 38 42 f8 5a 6e |...-mq2.i..8B.Zn|
> 000000a0 05 35 d6 94 41 c0 9f c7 ba 43 |.5..A....C|
> 000000aa
to reconstruct the file and check its sha1, and indeed it is fine.
So this bogus index was probably actually created by Git, not an
after-the-fact byte corruption.
-Peff
