CVE-2021-47089

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> kfence: fix memory leak when cat kfence objects<br /> <br /> Hulk robot reported a kmemleak problem:<br /> <br /> unreferenced object 0xffff93d1d8cc02e8 (size 248):<br /> comm "cat", pid 23327, jiffies 4624670141 (age 495992.217s)<br /> hex dump (first 32 bytes):<br /> 00 40 85 19 d4 93 ff ff 00 10 00 00 00 00 00 00 .@..............<br /> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................<br /> backtrace:<br /> seq_open+0x2a/0x80<br /> full_proxy_open+0x167/0x1e0<br /> do_dentry_open+0x1e1/0x3a0<br /> path_openat+0x961/0xa20<br /> do_filp_open+0xae/0x120<br /> do_sys_openat2+0x216/0x2f0<br /> do_sys_open+0x57/0x80<br /> do_syscall_64+0x33/0x40<br /> entry_SYSCALL_64_after_hwframe+0x44/0xa9<br /> unreferenced object 0xffff93d419854000 (size 4096):<br /> comm "cat", pid 23327, jiffies 4624670141 (age 495992.217s)<br /> hex dump (first 32 bytes):<br /> 6b 66 65 6e 63 65 2d 23 32 35 30 3a 20 30 78 30 kfence-#250: 0x0<br /> 30 30 30 30 30 30 30 37 35 34 62 64 61 31 32 2d 0000000754bda12-<br /> backtrace:<br /> seq_read_iter+0x313/0x440<br /> seq_read+0x14b/0x1a0<br /> full_proxy_read+0x56/0x80<br /> vfs_read+0xa5/0x1b0<br /> ksys_read+0xa0/0xf0<br /> do_syscall_64+0x33/0x40<br /> entry_SYSCALL_64_after_hwframe+0x44/0xa9<br /> <br /> I find that we can easily reproduce this problem with the following<br /> commands:<br /> <br /> cat /sys/kernel/debug/kfence/objects<br /> echo scan &gt; /sys/kernel/debug/kmemleak<br /> cat /sys/kernel/debug/kmemleak<br /> <br /> The leaked memory is allocated in the stack below:<br /> <br /> do_syscall_64<br /> do_sys_open<br /> do_dentry_open<br /> full_proxy_open<br /> seq_open ---&gt; alloc seq_file<br /> vfs_read<br /> full_proxy_read<br /> seq_read<br /> seq_read_iter<br /> traverse ---&gt; alloc seq_buf<br /> <br /> And it should have been released in the following process:<br /> <br /> do_syscall_64<br /> syscall_exit_to_user_mode<br /> exit_to_user_mode_prepare<br /> task_work_run<br /> ____fput<br /> __fput<br /> full_proxy_release ---&gt; free here<br /> <br /> However, the release function corresponding to file_operations is not<br /> implemented in kfence. As a result, a memory leak occurs. Therefore,<br /> the solution to this problem is to implement the corresponding release<br /> function.