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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id u67sm39861353qki.22.2019.01.11.12.59.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 11 Jan 2019 12:59:08 -0800 (PST) From: Qian Cai To: akpm@linux-foundation.org Cc: esploit@protonmail.ch, jejb@linux.ibm.com, dgilbert@interlog.com, martin.petersen@oracle.com, joeypabalinas@gmail.com, walken@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qian Cai Subject: [PATCH v2] rbtree: fix the red root Date: Fri, 11 Jan 2019 15:58:43 -0500 Message-Id: <20190111205843.25761-1-cai@lca.pw> X-Mailer: git-send-email 2.17.2 (Apple Git-113) In-Reply-To: <20190111181600.GJ6310@bombadil.infradead.org> References: <20190111181600.GJ6310@bombadil.infradead.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A GPF was reported, kasan: CONFIG_KASAN_INLINE enabled kasan: GPF could be caused by NULL-ptr deref or user memory access general protection fault: 0000 [#1] SMP KASAN kasan_die_handler.cold.22+0x11/0x31 notifier_call_chain+0x17b/0x390 atomic_notifier_call_chain+0xa7/0x1b0 notify_die+0x1be/0x2e0 do_general_protection+0x13e/0x330 general_protection+0x1e/0x30 rb_insert_color+0x189/0x1480 create_object+0x785/0xca0 kmemleak_alloc+0x2f/0x50 kmem_cache_alloc+0x1b9/0x3c0 getname_flags+0xdb/0x5d0 getname+0x1e/0x20 do_sys_open+0x3a1/0x7d0 __x64_sys_open+0x7e/0xc0 do_syscall_64+0x1b3/0x820 entry_SYSCALL_64_after_hwframe+0x49/0xbe It turned out, gparent = rb_red_parent(parent); tmp = gparent->rb_right; <-- GPF was triggered here. Apparently, "gparent" is NULL which indicates "parent" is rbtree's root which is red. Otherwise, it will be treated properly a few lines above. /* * If there is a black parent, we are done. * Otherwise, take some corrective action as, * per 4), we don't want a red root or two * consecutive red nodes. */ if(rb_is_black(parent)) break; Hence, it violates the rule #1 (the root can't be red) and need a fix up, and also add a regression test for it. This looks like was introduced by 6d58452dc06 where it no longer always paint the root as black. Fixes: 6d58452dc06 (rbtree: adjust root color in rb_insert_color() only when necessary) Reported-by: Esme Tested-by: Joey Pabalinas Signed-off-by: Qian Cai --- v2: add a regression test. lib/rbtree.c | 7 +++++++ lib/rbtree_test.c | 11 +++++++++++ 2 files changed, 18 insertions(+) diff --git a/lib/rbtree.c b/lib/rbtree.c index d3ff682fd4b8..acc969ad8de9 100644 --- a/lib/rbtree.c +++ b/lib/rbtree.c @@ -127,6 +127,13 @@ __rb_insert(struct rb_node *node, struct rb_root *root, break; gparent = rb_red_parent(parent); + if (unlikely(!gparent)) { + /* + * The root is red so correct it. + */ + rb_set_parent_color(parent, NULL, RB_BLACK); + break; + } tmp = gparent->rb_right; if (parent != tmp) { /* parent == gparent->rb_left */ diff --git a/lib/rbtree_test.c b/lib/rbtree_test.c index b7055b2a07d3..afad0213a117 100644 --- a/lib/rbtree_test.c +++ b/lib/rbtree_test.c @@ -345,6 +345,17 @@ static int __init rbtree_test_init(void) check(0); } + /* + * a little regression test to catch a bug may be introduced by + * 6d58452dc06 (rbtree: adjust root color in rb_insert_color() only when + * necessary) + */ + insert(nodes, &root); + nodes->rb.__rb_parent_color = RB_RED; + insert(nodes + 1, &root); + erase(nodes + 1, &root); + erase(nodes, &root); + printk(KERN_ALERT "augmented rbtree testing"); init(); -- 2.17.2 (Apple Git-113)