linux-kernel - Re: [PATCH] SPARC64: fix iommu sg chaining

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20071017.021305.74746838.davem@davemloft.net>
Date:	Wed, 17 Oct 2007 02:13:05 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jens.axboe@...cle.com
Cc:	fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH] SPARC64: fix iommu sg chaining

From: Jens Axboe <jens.axboe@...cle.com>
Date: Wed, 17 Oct 2007 10:45:28 +0200

> Righto, it's invalid to call sg_next() on the last entry!

Unfortunately, that's what the sparc64 code wanted to do, this
transformation in the sparc64 sg chaining patch is not equilavent:

-	struct scatterlist *sg_end = sg + nelems;
+	struct scatterlist *sg_end = sg_last(sg, nelems);
 ...
-			while (sg < sg_end &&
+			while (sg != sg_end &&

No, that's not what the code was doing.  The while loop
has to process the last entry in the list,

We really needed "sg_end" to be "one past the last element",
rather than "the last element".

Since you say that sg_next() on the last entry is illegal,
and that's what this code would have done to try and reach
loop termination (it doesn't actually derefrence that
"end plus one" scatterlist entry) I'll try to code this up
some other way.

Besides, sg_last() is so absurdly expensive, it has to walk the entire
chain in the chaining case.  So better to implement this without it.

I would suggest that other sg_last() uses be audited for the same bug.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/