linux-kernel - [PATCH] Fix thinko in iov_iter_single_seg

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-next>] [day] [month] [year] [list]

Date:	Thu, 13 Nov 2014 20:15:23 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] Fix thinko in iov_iter_single_seg_count

The branches of the if (i->type & ITER_BVEC) statement in
iov_iter_single_seg_count() are the wrong way around; if ITER_BVEC is
clear then we use i->bvec, when we should be using i->iov.  This fixes
it.

In my case, the symptom that this caused was that a KVM guest doing
filesystem operations on a virtual disk would result in one of qemu's
threads on the host going into an infinite loop in
generic_perform_write().  The loop would hit the copied == 0 case and
call iov_iter_single_seg_count() to reduce the number of bytes to try
to process, but because of the error, iov_iter_single_seg_count()
would just return i->count and the loop made no progress and continued
forever.

Cc: stable@...r.kernel.org # 3.16+
Signed-off-by: Paul Mackerras <paulus@...ba.org>
---
diff --git a/mm/iov_iter.c b/mm/iov_iter.c
index eafcf60..e34a3cb 100644
--- a/mm/iov_iter.c
+++ b/mm/iov_iter.c
@@ -911,9 +911,9 @@ size_t iov_iter_single_seg_count(const struct iov_iter *i)
 	if (i->nr_segs == 1)
 		return i->count;
 	else if (i->type & ITER_BVEC)
-		return min(i->count, i->iov->iov_len - i->iov_offset);
-	else
 		return min(i->count, i->bvec->bv_len - i->iov_offset);
+	else
+		return min(i->count, i->iov->iov_len - i->iov_offset);
 }
 EXPORT_SYMBOL(iov_iter_single_seg_count);

--
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/