linux-kernel - [PATCH 4.19 79/88] mm: slub: fix conversion of freelist

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Date:   Tue,  8 Sep 2020 17:26:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eugeniu Rosca <erosca@...adit-jv.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dongli Zhang <dongli.zhang@...cle.com>,
        Joe Jin <joe.jin@...cle.com>, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.19 79/88] mm: slub: fix conversion of freelist_corrupted()

From: Eugeniu Rosca <erosca@...adit-jv.com>

commit dc07a728d49cf025f5da2c31add438d839d076c0 upstream.

Commit 52f23478081ae0 ("mm/slub.c: fix corrupted freechain in
deactivate_slab()") suffered an update when picked up from LKML [1].

Specifically, relocating 'freelist = NULL' into 'freelist_corrupted()'
created a no-op statement.  Fix it by sticking to the behavior intended
in the original patch [1].  In addition, make freelist_corrupted()
immune to passing NULL instead of &freelist.

The issue has been spotted via static analysis and code review.

[1] https://lore.kernel.org/linux-mm/20200331031450.12182-1-dongli.zhang@oracle.com/

Fixes: 52f23478081ae0 ("mm/slub.c: fix corrupted freechain in deactivate_slab()")
Signed-off-by: Eugeniu Rosca <erosca@...adit-jv.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dongli Zhang <dongli.zhang@...cle.com>
Cc: Joe Jin <joe.jin@...cle.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Pekka Enberg <penberg@...nel.org>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: <stable@...r.kernel.org>
Link: https://lkml.kernel.org/r/20200824130643.10291-1-erosca@de.adit-jv.com
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/slub.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -646,12 +646,12 @@ static void slab_fix(struct kmem_cache *
 }
 
 static bool freelist_corrupted(struct kmem_cache *s, struct page *page,
-			       void *freelist, void *nextfree)
+			       void **freelist, void *nextfree)
 {
 	if ((s->flags & SLAB_CONSISTENCY_CHECKS) &&
-	    !check_valid_pointer(s, page, nextfree)) {
-		object_err(s, page, freelist, "Freechain corrupt");
-		freelist = NULL;
+	    !check_valid_pointer(s, page, nextfree) && freelist) {
+		object_err(s, page, *freelist, "Freechain corrupt");
+		*freelist = NULL;
 		slab_fix(s, "Isolate corrupted freechain");
 		return true;
 	}
@@ -1343,7 +1343,7 @@ static inline void dec_slabs_node(struct
 							int objects) {}
 
 static bool freelist_corrupted(struct kmem_cache *s, struct page *page,
-			       void *freelist, void *nextfree)
+			       void **freelist, void *nextfree)
 {
 	return false;
 }
@@ -2037,7 +2037,7 @@ static void deactivate_slab(struct kmem_
 		 * 'freelist' is already corrupted.  So isolate all objects
 		 * starting at 'freelist'.
 		 */
-		if (freelist_corrupted(s, page, freelist, nextfree))
+		if (freelist_corrupted(s, page, &freelist, nextfree))
 			break;
 
 		do {