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From: Nicolas Pitre <>
To: Linus Torvalds <>
Cc: Alexander Litvinov <>,
	Git Mailing List <>
Subject: Re: My git repo is broken, how to fix it ?
Date: Thu, 22 Mar 2007 12:34:02 -0400 (EDT)	[thread overview]
Message-ID: <alpine.LFD.0.83.0703221215150.18328@xanadu.home> (raw)
In-Reply-To: <>

On Thu, 22 Mar 2007, Linus Torvalds wrote:

> Ok, apart from #1, those should be in current -git now, along with better 
> validation checks (by Nico) when packing. So hopefully at least when there 
> is corruption in a loose object, we will now always notice when we do a 
> "git repack", and will never generate a broken pack-file. Knock wood.

Not yet actually.  What I did do is to make index-pack perform more 
validation and ensure it never accept SHA1 collisions.

For the repack case... I think there should be a better way.  Either we 
revalidate the full SHA1 which would be expensive as we'd basically lose 
most advantages of direct pack data copy.

What I'm pondering is some sort of lightweight checksum like adler32 for 
object data in the pack but stored in the index.  Since index-pack 
already perform the full SHA1 already, it could as well provide a 
checksum for the raw pack object data for the repack case.  Currently we 
try to validate reused pack data by attempting an inflate pass on the 
object payload, but that doesn't validate the object type nor the 
reference SHA1 to delta base objects which could get corrupted and 
copied without noticing into another pack.

> Of course, I actually wonder if the bug might be in your version of zlib 
> (miscompiled or some other thing), in which case *any* amount of 
> pre-validation won't really help, because it will become corrupted when we 
> deflate it prior to writing. For example, if "deflateBound()" sometimes 
> doesn't give a valid upper bound and we allocate too little space..

Well, since we provide the size of the allocated output buffer to zlib 
it would be seriously broken if it overflowed it.  Also zlib perform a 
checksum verification of the deflated data if I remember correctly.  So 
it seems to me that zlib should be quite self validating already.


  reply	other threads:[~2007-03-22 16:34 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-28  4:36 My git repo is broken, how to fix it ? Alexander Litvinov
2007-02-28  4:57 ` Linus Torvalds
2007-02-28 11:54   ` Alexander Litvinov
2007-02-28 16:19     ` Linus Torvalds
2007-02-28 19:12       ` Alex Riesen
2007-03-19 13:32       ` Alexander Litvinov
2007-03-19 15:20         ` Linus Torvalds
     [not found]           ` <>
2007-03-20  5:34             ` Linus Torvalds
2007-03-20  6:55               ` Alexander Litvinov
2007-03-20  7:42               ` Junio C Hamano
2007-03-20 15:23                 ` Nicolas Pitre
     [not found] ` <>
     [not found]   ` <>
     [not found]     ` <>
2007-03-22 15:58       ` Linus Torvalds
2007-03-22 16:34         ` Nicolas Pitre [this message]
     [not found]       ` <>
2007-03-22 16:17         ` Linus Torvalds
2007-03-22 16:29           ` Linus Torvalds
2007-03-22 16:48             ` Linus Torvalds
2007-03-22 17:01               ` Nicolas Pitre
2007-03-22 17:10                 ` Linus Torvalds
2007-03-22 17:28                   ` Nicolas Pitre
2007-03-22 22:13                   ` Jeff King
2007-03-23  0:25                     ` Linus Torvalds
2007-03-23  0:42                       ` Bill Lear
2007-03-23  0:51                       ` Jeff King
2007-03-22 20:31               ` [PATCH] git-apply: Do not free the wrong buffer when we convert the data for writeout Junio C Hamano
2007-03-22 20:55                 ` Linus Torvalds
2007-03-23  3:55                   ` Alexander Litvinov
2007-03-23  3:40               ` My git repo is broken, how to fix it ? Alexander Litvinov
2007-03-22 17:12             ` Johannes Sixt
2021-06-06 17:27 B
2021-06-06 17:28 B
2021-12-25  8:30 Joseph Mitchell
2021-12-26  0:48 ` Lemuria
2023-05-29 18:57 ross thomas

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