padata: use integer wrap around to prevent deadlock on seq_nr overflow

JIRA: https://issues.redhat.com/browse/RHEL-63240
CVE: CVE-2024-47739

commit 9a22b28
Author: VanGiang Nguyen <vangiang.nguyen@rohde-schwarz.com>
Date:   Fri Aug 9 06:21:42 2024 +0000

    padata: use integer wrap around to prevent deadlock on seq_nr overflow

    When submitting more than 2^32 padata objects to padata_do_serial, the
    current sorting implementation incorrectly sorts padata objects with
    overflowed seq_nr, causing them to be placed before existing objects in
    the reorder list. This leads to a deadlock in the serialization process
    as padata_find_next cannot match padata->seq_nr and pd->processed
    because the padata instance with overflowed seq_nr will be selected
    next.

    To fix this, we use an unsigned integer wrap around to correctly sort
    padata objects in scenarios with integer overflow.

    Fixes: bfde23c ("padata: unbind parallel jobs from specific CPUs")
    Cc: <stable@vger.kernel.org>
    Co-developed-by: Christian Gafert <christian.gafert@rohde-schwarz.com>
    Signed-off-by: Christian Gafert <christian.gafert@rohde-schwarz.com>
    Co-developed-by: Max Ferger <max.ferger@rohde-schwarz.com>
    Signed-off-by: Max Ferger <max.ferger@rohde-schwarz.com>
    Signed-off-by: Van Giang Nguyen <vangiang.nguyen@rohde-schwarz.com>
    Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Radostin Stoyanov <radostin@redhat.com>

Author: rst0git

kernel/padata.c

@@ -404,7 +404,8 @@ void padata_do_serial(struct padata_priv *padata)
 	/* Sort in ascending order of sequence number. */
 	list_for_each_prev(pos, &reorder->list) {
 		cur = list_entry(pos, struct padata_priv, list);
-		if (cur->seq_nr < padata->seq_nr)
+		/* Compare by difference to consider integer wrap around */
+		if ((signed int)(cur->seq_nr - padata->seq_nr) < 0)
 			break;
 	}
 	list_add(&padata->list, pos);