LinuxLists.cc - [PATCH -next] kfence: fix memory leak when cat kfence objects

2021-12-06 13:24:35

Subject: [PATCH -next] kfence: fix memory leak when cat kfence objects

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 <[email protected]>
Signed-off-by: Baokun Li <[email protected]>
---
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

2021-12-06 13:29:45

by Marco Elver

[permalink] [raw]

Subject: Re: [PATCH -next] kfence: fix memory leak when cat kfence objects

On Mon, 6 Dec 2021 at 14:24, Baokun Li <[email protected]> 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 <[email protected]>
> Signed-off-by: Baokun Li <[email protected]>

Good catch!

Acked-by: Marco Elver <[email protected]>

> ---
> 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
>

2021-12-06 14:07:34

by Kefeng Wang

[permalink] [raw]

Subject: Re: [PATCH -next] kfence: fix memory leak when cat kfence objects

On 2021/12/6 21:29, Marco Elver wrote:
> On Mon, 6 Dec 2021 at 14:24, Baokun Li <[email protected]> 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 <[email protected]>
>> Signed-off-by: Baokun Li <[email protected]>
Reviewed-by: Kefeng Wang <[email protected]>