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From:   Qian Cai <cai@lca.pw>
To:     akpm@linux-foundation.org
Cc:     cl@linux.com, penberg@kernel.org, rientjes@google.com,
        iamjoonsoo.kim@lge.com, tj@kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Qian Cai <cai@lca.pw>
Subject: [PATCH] slab: fix a crash by reading /proc/slab_allocators
Date:   Sat,  6 Apr 2019 18:59:01 -0400
Message-Id: <20190406225901.35465-1-cai@lca.pw>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The commit 510ded33e075 ("slab: implement slab_root_caches list")
changes the name of the list node within "struct kmem_cache" from
"list" to "root_caches_node", but leaks_show() still use the "list"
which causes a crash when reading /proc/slab_allocators.

BUG: unable to handle kernel NULL pointer dereference at
00000000000000aa
PGD 0 P4D 0
Oops: 0000 [#1] SMP DEBUG_PAGEALLOC PTI
CPU: 3 PID: 5925 Comm: ldd Not tainted 5.1.0-rc3-mm1+ #6
RIP: 0010:__lock_acquire.isra.14+0x4b4/0xa50
Call Trace:
 <IRQ>
 lock_acquire+0xa3/0x180
 _raw_spin_lock+0x2f/0x40
 do_drain+0x61/0xc0
 flush_smp_call_function_queue+0x3a/0x110
 generic_smp_call_function_single_interrupt+0x13/0x2b
 smp_call_function_interrupt+0x66/0x1a0
 call_function_interrupt+0xf/0x20
 </IRQ>
RIP: 0010:__tlb_remove_page_size+0x8c/0xe0
 zap_pte_range+0x39f/0xc80
 unmap_page_range+0x38a/0x550
 unmap_single_vma+0x7d/0xe0
 unmap_vmas+0xae/0xd0
 exit_mmap+0xae/0x190
 mmput+0x7a/0x150
 do_exit+0x2d9/0xd40
 do_group_exit+0x41/0xd0
 __x64_sys_exit_group+0x18/0x20
 do_syscall_64+0x68/0x381
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 510ded33e075 ("slab: implement slab_root_caches list")
Signed-off-by: Qian Cai <cai@lca.pw>
---
 mm/slab.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index 46a6e084222b..9142ee992493 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4307,7 +4307,8 @@ static void show_symbol(struct seq_file *m, unsigned long address)
 
 static int leaks_show(struct seq_file *m, void *p)
 {
-	struct kmem_cache *cachep = list_entry(p, struct kmem_cache, list);
+	struct kmem_cache *cachep = list_entry(p, struct kmem_cache,
+					       root_caches_node);
 	struct page *page;
 	struct kmem_cache_node *n;
 	const char *name;
-- 
2.17.2 (Apple Git-113)