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Mon, 06 Dec 2021 05:29:42 -0800 (PST) MIME-Version: 1.0 References: <20211206133628.2822545-1-libaokun1@huawei.com> In-Reply-To: <20211206133628.2822545-1-libaokun1@huawei.com> From: Marco Elver Date: Mon, 6 Dec 2021 14:29:31 +0100 Message-ID: Subject: Re: [PATCH -next] kfence: fix memory leak when cat kfence objects To: Baokun Li Cc: glider@google.com, dvyukov@google.com, akpm@linux-foundation.org, viro@zeniv.linux.org.uk, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yukuai3@huawei.com, Hulk Robot Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 6 Dec 2021 at 14:24, Baokun Li wrote: > > Hulk robot reported a kmemleak problem: > ----------------------------------------------------------------------- > unreferenced object 0xffff93d1d8cc02e8 (size 248): > comm "cat", pid 23327, jiffies 4624670141 (age 495992.217s) > hex dump (first 32 bytes): > 00 40 85 19 d4 93 ff ff 00 10 00 00 00 00 00 00 .@.............. > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > backtrace: > [<00000000db5610b3>] seq_open+0x2a/0x80 > [<00000000d66ac99d>] full_proxy_open+0x167/0x1e0 > [<00000000d58ef917>] do_dentry_open+0x1e1/0x3a0 > [<0000000016c91867>] path_openat+0x961/0xa20 > [<00000000909c9564>] do_filp_open+0xae/0x120 > [<0000000059c761e6>] do_sys_openat2+0x216/0x2f0 > [<00000000b7a7b239>] do_sys_open+0x57/0x80 > [<00000000e559d671>] do_syscall_64+0x33/0x40 > [<000000000ea1fbfd>] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > unreferenced object 0xffff93d419854000 (size 4096): > comm "cat", pid 23327, jiffies 4624670141 (age 495992.217s) > hex dump (first 32 bytes): > 6b 66 65 6e 63 65 2d 23 32 35 30 3a 20 30 78 30 kfence-#250: 0x0 > 30 30 30 30 30 30 30 37 35 34 62 64 61 31 32 2d 0000000754bda12- > backtrace: > [<000000008162c6f2>] seq_read_iter+0x313/0x440 > [<0000000020b1b3e3>] seq_read+0x14b/0x1a0 > [<00000000af248fbc>] full_proxy_read+0x56/0x80 > [<00000000f97679d1>] vfs_read+0xa5/0x1b0 > [<000000000ed8a36f>] ksys_read+0xa0/0xf0 > [<00000000e559d671>] do_syscall_64+0x33/0x40 > [<000000000ea1fbfd>] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > ----------------------------------------------------------------------- > > I find that we can easily reproduce this problem with the following > commands: > `cat /sys/kernel/debug/kfence/objects` > `echo scan > /sys/kernel/debug/kmemleak` > `cat /sys/kernel/debug/kmemleak` > > The leaked memory is allocated in the stack below: > ---------------------------------- > do_syscall_64 > do_sys_open > do_dentry_open > full_proxy_open > seq_open ---> alloc seq_file > vfs_read > full_proxy_read > seq_read > seq_read_iter > traverse ---> alloc seq_buf > ---------------------------------- > > And it should have been released in the following process: > ---------------------------------- > do_syscall_64 > syscall_exit_to_user_mode > exit_to_user_mode_prepare > task_work_run > ____fput > __fput > full_proxy_release ---> free here > ---------------------------------- > > However, the release function corresponding to file_operations is not > implemented in kfence. As a result, a memory leak occurs. Therefore, > the solution to this problem is to implement the corresponding > release function. > > Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure") > Reported-by: Hulk Robot > Signed-off-by: Baokun Li Good catch! Acked-by: Marco Elver > --- > mm/kfence/core.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/kfence/core.c b/mm/kfence/core.c > index 46103a7628a6..186838f062b2 100644 > --- a/mm/kfence/core.c > +++ b/mm/kfence/core.c > @@ -684,6 +684,7 @@ static const struct file_operations objects_fops = { > .open = open_objects, > .read = seq_read, > .llseek = seq_lseek, > + .release = seq_release, > }; > > static int __init kfence_debugfs_init(void) > -- > 2.31.1 >