From: Jann Horn <jannh@google.com>
Date: Tue, 17 Mar 2020 01:28:45 +0100
Subject: mm: slub: add missing TID bump in kmem_cache_alloc_bulk()
Git-commit: fd4d9c7d0c71866ec0c2825189ebd2ce35bd95b8
Patch-mainline: v5.6-rc7
References: CVE-2020-29370, bsc#1179435, bsc#1167657, VM functionality

When kmem_cache_alloc_bulk() attempts to allocate N objects from a percpu
freelist of length M, and N > M > 0, it will first remove the M elements
from the percpu freelist, then call ___slab_alloc() to allocate the next
element and repopulate the percpu freelist. ___slab_alloc() can re-enable
IRQs via allocate_slab(), so the TID must be bumped before ___slab_alloc()
to properly commit the freelist head change.

Fix it by unconditionally bumping c->tid when entering the slowpath.

Cc: stable@vger.kernel.org
Fixes: ebe909e0fdb3 ("slub: improve bulk alloc strategy")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/slub.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3154,6 +3154,15 @@ int kmem_cache_alloc_bulk(struct kmem_ca
 
 		if (unlikely(!object)) {
 			/*
+			 * We may have removed an object from c->freelist using
+			 * the fastpath in the previous iteration; in that case,
+			 * c->tid has not been bumped yet.
+			 * Since ___slab_alloc() may reenable interrupts while
+			 * allocating memory, we should bump c->tid now.
+			 */
+			c->tid = next_tid(c->tid);
+
+			/*
 			 * Invoking slow path likely have side-effect
 			 * of re-populating per CPU c->freelist
 			 */