This is a note to let you know that I've just added the patch titled kfence: fix memory leak when cat kfence objects to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kfence-fix-memory-leak-when-cat-kfence-objects.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 0129ab1f268b6cf88825eae819b9b84aa0a85634 Mon Sep 17 00:00:00 2001 From: Baokun Li <libaokun1@xxxxxxxxxx> Date: Fri, 24 Dec 2021 21:12:32 -0800 Subject: kfence: fix memory leak when cat kfence objects From: Baokun Li <libaokun1@xxxxxxxxxx> commit 0129ab1f268b6cf88825eae819b9b84aa0a85634 upstream. 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: seq_open+0x2a/0x80 full_proxy_open+0x167/0x1e0 do_dentry_open+0x1e1/0x3a0 path_openat+0x961/0xa20 do_filp_open+0xae/0x120 do_sys_openat2+0x216/0x2f0 do_sys_open+0x57/0x80 do_syscall_64+0x33/0x40 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: seq_read_iter+0x313/0x440 seq_read+0x14b/0x1a0 full_proxy_read+0x56/0x80 vfs_read+0xa5/0x1b0 ksys_read+0xa0/0xf0 do_syscall_64+0x33/0x40 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. Link: https://lkml.kernel.org/r/20211206133628.2822545-1-libaokun1@xxxxxxxxxx Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure") Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx> Acked-by: Marco Elver <elver@xxxxxxxxxx> Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Yu Kuai <yukuai3@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/kfence/core.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -578,6 +578,7 @@ static const struct file_operations obje .open = open_objects, .read = seq_read, .llseek = seq_lseek, + .release = seq_release, }; static int __init kfence_debugfs_init(void) Patches currently in stable-queue which might be from libaokun1@xxxxxxxxxx are queue-5.15/kfence-fix-memory-leak-when-cat-kfence-objects.patch