Commit d2e7276b authored Feb 22, 2010 by Tejun Heo Committed by Linus Torvalds Feb 22, 2010

idr: fix a critical misallocation bug, take#2



This is retry of reverted 859ddf09
("idr: fix a critical misallocation bug") which contained two bugs.

* pa[idp->layers] should be cleared even if it's not used by
  sub_alloc() because it's used by mark idr_mark_full().

* The original condition check also assigned pa[l] to p which the new
  code didn't do thus leaving p pointing at the wrong layer.

Both problems have been fixed and the idr code has received good amount
testing using userland testing setup where simple bitmap allocator is
run parallel to verify the result of idr allocation.

The bug this patch fixes is caused by sub_alloc() optimization path
bypassing out-of-room condition check and restarting allocation loop
with starting value higher than maximum allowed value.  For detailed
description, please read commit message of 859ddf09.

Signed-off-by: Tejun Heo <tj@kernel.org>
Based-on-patch-from: Eric Paris <eparis@redhat.com>
Reported-by: Eric Paris <eparis@redhat.com>
Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Tested-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 70118837

lib/idr.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -156,10 +156,12 @@ static int sub_alloc(struct idr idp, int starting_id, struct idr_layer **pa)
		id = (id \| ((1 << (IDR_BITS * l)) - 1)) + 1;

		/* if already at the top layer, we need to grow */
		if (!(p = pa[l])) {
		if (id >= 1 << (idp->layers * IDR_BITS)) {
		*starting_id = id;
		return IDR_NEED_TO_GROW;
		}
		p = pa[l];
		BUG_ON(!p);

		/* If we need to go up one layer, continue the
		* loop; otherwise, restart from the top.

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