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SubjectRe: [PATCH -next] kfence: fix memory leak when cat kfence objects
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On 2021/12/6 21:29, Marco Elver wrote:
> On Mon, 6 Dec 2021 at 14:24, Baokun Li <libaokun1@huawei.com> 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 <hulkci@huawei.com>
>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>

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