Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Dmitry Vyukov]

On Sun, Jan 21, 2018 at 6:54 PM, Shankara Pailoor  wrote:
> Below is a reproducer.
>
> #define _GNU_SOURCE
> #include 
> #include 
> #include 
> #include 
> #include 
>
> #define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
> #define KCOV_ENABLE _IO('c', 100)
> #define KCOV_DISABLE _IO('c', 101)
> #define COVER_SIZE (16 << 20)
>
>
> void kcov_setup() {
> unsigned long *cover;
> int fd;
>
> fd = open("/sys/kernel/debug/kcov", O_RDWR);
> if (fd == -1)
> perror("open"), exit(1);
> if (ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE))
> perror("ioctl"), exit(1);
> cover = (unsigned long*)mmap(NULL,
> COVER_SIZE * sizeof(unsigned long),
> PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> if ((void*)cover == MAP_FAILED)
> perror("mmap"), exit(1);
> if (ioctl(fd, KCOV_ENABLE, 0))
> perror("ioctl"), exit(1);
>
> }
>
> void main() {
> int i;
> for (i = 0; i < 4; i++)
> kcov_setup();
> sleep(10);
> }


Thanks!

I've just mailed a fix for this:
https://groups.google.com/d/msg/syzkaller/Hclbq5Elfs8/J5V_FnC4DgAJ

With that patch the second KCOV_ENABLE return EBUSY.
To make it clear, it won't fix your code per se, because it's a misuse
of the API. You need to either call KCOV_DISABLE first, or reuse the
first kcov descriptor and mapping, you can just write 0 to the first
work of the mapping to reset current coverage (which should be much
faster).

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Dmitry Vyukov]

On Sun, Jan 21, 2018 at 6:54 PM, Shankara Pailoor  wrote:
> Below is a reproducer.
>
> #define _GNU_SOURCE
> #include 
> #include 
> #include 
> #include 
> #include 
>
> #define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
> #define KCOV_ENABLE _IO('c', 100)
> #define KCOV_DISABLE _IO('c', 101)
> #define COVER_SIZE (16 << 20)
>
>
> void kcov_setup() {
> unsigned long *cover;
> int fd;
>
> fd = open("/sys/kernel/debug/kcov", O_RDWR);
> if (fd == -1)
> perror("open"), exit(1);
> if (ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE))
> perror("ioctl"), exit(1);
> cover = (unsigned long*)mmap(NULL,
> COVER_SIZE * sizeof(unsigned long),
> PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> if ((void*)cover == MAP_FAILED)
> perror("mmap"), exit(1);
> if (ioctl(fd, KCOV_ENABLE, 0))
> perror("ioctl"), exit(1);
>
> }
>
> void main() {
> int i;
> for (i = 0; i < 4; i++)
> kcov_setup();
> sleep(10);
> }


Thanks!

I've just mailed a fix for this:
https://groups.google.com/d/msg/syzkaller/Hclbq5Elfs8/J5V_FnC4DgAJ

With that patch the second KCOV_ENABLE return EBUSY.
To make it clear, it won't fix your code per se, because it's a misuse
of the API. You need to either call KCOV_DISABLE first, or reuse the
first kcov descriptor and mapping, you can just write 0 to the first
work of the mapping to reset current coverage (which should be much
faster).

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Shankara Pailoor]

Below is a reproducer.

#define _GNU_SOURCE
#include 
#include 
#include 
#include 
#include 

#define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
#define KCOV_ENABLE _IO('c', 100)
#define KCOV_DISABLE _IO('c', 101)
#define COVER_SIZE (16 << 20)


void kcov_setup() {
unsigned long *cover;
int fd;

fd = open("/sys/kernel/debug/kcov", O_RDWR);
if (fd == -1)
perror("open"), exit(1);
if (ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE))
perror("ioctl"), exit(1);
cover = (unsigned long*)mmap(NULL,
COVER_SIZE * sizeof(unsigned long),
PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if ((void*)cover == MAP_FAILED)
perror("mmap"), exit(1);
if (ioctl(fd, KCOV_ENABLE, 0))
perror("ioctl"), exit(1);

}

void main() {
int i;
for (i = 0; i < 4; i++)
kcov_setup();
sleep(10);
}

On Sun, Jan 21, 2018 at 1:11 AM, Shankara Pailoor  wrote:
> Hi Dmitry,
>
> The leaks went away when I disabled and closed the old file
> descriptors before opening new ones.
>
> The patch you sent wouldn't work because t is not initialized at the
> line. This seems to work for me
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 7594c03..1397006 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -371,6 +371,8 @@ static int kcov_ioctl_locked(struct kcov *kcov,
> unsigned int cmd,
> else
> return -EINVAL;
> t = current;
> +  if (!t->kcov)
> +   return -EBUSY;
> /* Cache in task struct for performance. */
> t->kcov_size = kcov->size;
> t->kcov_area = kcov->area;
>
> On Sat, Jan 20, 2018 at 7:06 AM, Dmitry Vyukov  wrote:
>> On Sat, Jan 20, 2018 at 4:01 PM, Shankara Pailoor  
>> wrote:
>>> Hi Dmitry,
>>>
>>> I will try and get something to you tomorrow. Just wondering, but what
>>> happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
>>> twice? I am looking here
>>> https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
>>> and I don't see where the previous struct would get freed.
>>
>> Good question. Perhaps we need something like:
>>
>> diff --git a/kernel/kcov.c b/kernel/kcov.c
>> index 7594c033d98a..c76498018500 100644
>> --- a/kernel/kcov.c
>> +++ b/kernel/kcov.c
>> @@ -358,7 +358,7 @@ static int kcov_ioctl_locked(struct kcov *kcov,
>> unsigned int cmd,
>>  */
>> if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
>> return -EINVAL;
>> -   if (kcov->t != NULL)
>> +   if (kcov->t != NULL || t->kcov != NULL)
>> return -EBUSY;
>> if (arg == KCOV_TRACE_PC)
>> kcov->mode = KCOV_MODE_TRACE_PC;
>>
>>
>>
>>> On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov  wrote:
 On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  
 wrote:
> Hi Dmitry,
>
> I added support for kcov in strace and I have been tracing a fairly
> large program but after a little while, I notice that when I mmap a
> new cover buffer, the call fails with ENOMEM. After killing the
> program, I try and rerun and I notice that there is nearly no memory
> on the system. When I do a kmemleak scan I get the following reports:
>
> I believe the problem occurs when I try and setup the kcov buffer
> again after an exec. Instead of reusing the old file descriptor I open
> kcov again within that process. In that case, I don't know what
> happens to the old kcov struct.
>
> I don't see a maintainers list for kcov so I decided to email you
> directly. Let me know what more information I can provide.


 Hi Shankara,

 Looks bad. Can you provide a reproducer?
 We extensively use kcov with syzkaller, but have not observed such
 leaks. Also I don't see anything obvious in the code.

 Thanks
>>>

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Shankara Pailoor]

Below is a reproducer.

#define _GNU_SOURCE
#include 
#include 
#include 
#include 
#include 

#define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
#define KCOV_ENABLE _IO('c', 100)
#define KCOV_DISABLE _IO('c', 101)
#define COVER_SIZE (16 << 20)


void kcov_setup() {
unsigned long *cover;
int fd;

fd = open("/sys/kernel/debug/kcov", O_RDWR);
if (fd == -1)
perror("open"), exit(1);
if (ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE))
perror("ioctl"), exit(1);
cover = (unsigned long*)mmap(NULL,
COVER_SIZE * sizeof(unsigned long),
PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if ((void*)cover == MAP_FAILED)
perror("mmap"), exit(1);
if (ioctl(fd, KCOV_ENABLE, 0))
perror("ioctl"), exit(1);

}

void main() {
int i;
for (i = 0; i < 4; i++)
kcov_setup();
sleep(10);
}

On Sun, Jan 21, 2018 at 1:11 AM, Shankara Pailoor  wrote:
> Hi Dmitry,
>
> The leaks went away when I disabled and closed the old file
> descriptors before opening new ones.
>
> The patch you sent wouldn't work because t is not initialized at the
> line. This seems to work for me
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 7594c03..1397006 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -371,6 +371,8 @@ static int kcov_ioctl_locked(struct kcov *kcov,
> unsigned int cmd,
> else
> return -EINVAL;
> t = current;
> +  if (!t->kcov)
> +   return -EBUSY;
> /* Cache in task struct for performance. */
> t->kcov_size = kcov->size;
> t->kcov_area = kcov->area;
>
> On Sat, Jan 20, 2018 at 7:06 AM, Dmitry Vyukov  wrote:
>> On Sat, Jan 20, 2018 at 4:01 PM, Shankara Pailoor  
>> wrote:
>>> Hi Dmitry,
>>>
>>> I will try and get something to you tomorrow. Just wondering, but what
>>> happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
>>> twice? I am looking here
>>> https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
>>> and I don't see where the previous struct would get freed.
>>
>> Good question. Perhaps we need something like:
>>
>> diff --git a/kernel/kcov.c b/kernel/kcov.c
>> index 7594c033d98a..c76498018500 100644
>> --- a/kernel/kcov.c
>> +++ b/kernel/kcov.c
>> @@ -358,7 +358,7 @@ static int kcov_ioctl_locked(struct kcov *kcov,
>> unsigned int cmd,
>>  */
>> if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
>> return -EINVAL;
>> -   if (kcov->t != NULL)
>> +   if (kcov->t != NULL || t->kcov != NULL)
>> return -EBUSY;
>> if (arg == KCOV_TRACE_PC)
>> kcov->mode = KCOV_MODE_TRACE_PC;
>>
>>
>>
>>> On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov  wrote:
 On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  
 wrote:
> Hi Dmitry,
>
> I added support for kcov in strace and I have been tracing a fairly
> large program but after a little while, I notice that when I mmap a
> new cover buffer, the call fails with ENOMEM. After killing the
> program, I try and rerun and I notice that there is nearly no memory
> on the system. When I do a kmemleak scan I get the following reports:
>
> I believe the problem occurs when I try and setup the kcov buffer
> again after an exec. Instead of reusing the old file descriptor I open
> kcov again within that process. In that case, I don't know what
> happens to the old kcov struct.
>
> I don't see a maintainers list for kcov so I decided to email you
> directly. Let me know what more information I can provide.


 Hi Shankara,

 Looks bad. Can you provide a reproducer?
 We extensively use kcov with syzkaller, but have not observed such
 leaks. Also I don't see anything obvious in the code.

 Thanks
>>>

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Shankara Pailoor]

Hi Dmitry,

The leaks went away when I disabled and closed the old file
descriptors before opening new ones.

The patch you sent wouldn't work because t is not initialized at the
line. This seems to work for me

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 7594c03..1397006 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -371,6 +371,8 @@ static int kcov_ioctl_locked(struct kcov *kcov,
unsigned int cmd,
else
return -EINVAL;
t = current;
+  if (!t->kcov)
+   return -EBUSY;
/* Cache in task struct for performance. */
t->kcov_size = kcov->size;
t->kcov_area = kcov->area;

On Sat, Jan 20, 2018 at 7:06 AM, Dmitry Vyukov  wrote:
> On Sat, Jan 20, 2018 at 4:01 PM, Shankara Pailoor  wrote:
>> Hi Dmitry,
>>
>> I will try and get something to you tomorrow. Just wondering, but what
>> happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
>> twice? I am looking here
>> https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
>> and I don't see where the previous struct would get freed.
>
> Good question. Perhaps we need something like:
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 7594c033d98a..c76498018500 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -358,7 +358,7 @@ static int kcov_ioctl_locked(struct kcov *kcov,
> unsigned int cmd,
>  */
> if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
> return -EINVAL;
> -   if (kcov->t != NULL)
> +   if (kcov->t != NULL || t->kcov != NULL)
> return -EBUSY;
> if (arg == KCOV_TRACE_PC)
> kcov->mode = KCOV_MODE_TRACE_PC;
>
>
>
>> On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov  wrote:
>>> On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  
>>> wrote:
 Hi Dmitry,

 I added support for kcov in strace and I have been tracing a fairly
 large program but after a little while, I notice that when I mmap a
 new cover buffer, the call fails with ENOMEM. After killing the
 program, I try and rerun and I notice that there is nearly no memory
 on the system. When I do a kmemleak scan I get the following reports:

 I believe the problem occurs when I try and setup the kcov buffer
 again after an exec. Instead of reusing the old file descriptor I open
 kcov again within that process. In that case, I don't know what
 happens to the old kcov struct.

 I don't see a maintainers list for kcov so I decided to email you
 directly. Let me know what more information I can provide.
>>>
>>>
>>> Hi Shankara,
>>>
>>> Looks bad. Can you provide a reproducer?
>>> We extensively use kcov with syzkaller, but have not observed such
>>> leaks. Also I don't see anything obvious in the code.
>>>
>>> Thanks
>>

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Shankara Pailoor]

Hi Dmitry,

The leaks went away when I disabled and closed the old file
descriptors before opening new ones.

The patch you sent wouldn't work because t is not initialized at the
line. This seems to work for me

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 7594c03..1397006 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -371,6 +371,8 @@ static int kcov_ioctl_locked(struct kcov *kcov,
unsigned int cmd,
else
return -EINVAL;
t = current;
+  if (!t->kcov)
+   return -EBUSY;
/* Cache in task struct for performance. */
t->kcov_size = kcov->size;
t->kcov_area = kcov->area;

On Sat, Jan 20, 2018 at 7:06 AM, Dmitry Vyukov  wrote:
> On Sat, Jan 20, 2018 at 4:01 PM, Shankara Pailoor  wrote:
>> Hi Dmitry,
>>
>> I will try and get something to you tomorrow. Just wondering, but what
>> happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
>> twice? I am looking here
>> https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
>> and I don't see where the previous struct would get freed.
>
> Good question. Perhaps we need something like:
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 7594c033d98a..c76498018500 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -358,7 +358,7 @@ static int kcov_ioctl_locked(struct kcov *kcov,
> unsigned int cmd,
>  */
> if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
> return -EINVAL;
> -   if (kcov->t != NULL)
> +   if (kcov->t != NULL || t->kcov != NULL)
> return -EBUSY;
> if (arg == KCOV_TRACE_PC)
> kcov->mode = KCOV_MODE_TRACE_PC;
>
>
>
>> On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov  wrote:
>>> On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  
>>> wrote:
 Hi Dmitry,

 I added support for kcov in strace and I have been tracing a fairly
 large program but after a little while, I notice that when I mmap a
 new cover buffer, the call fails with ENOMEM. After killing the
 program, I try and rerun and I notice that there is nearly no memory
 on the system. When I do a kmemleak scan I get the following reports:

 I believe the problem occurs when I try and setup the kcov buffer
 again after an exec. Instead of reusing the old file descriptor I open
 kcov again within that process. In that case, I don't know what
 happens to the old kcov struct.

 I don't see a maintainers list for kcov so I decided to email you
 directly. Let me know what more information I can provide.
>>>
>>>
>>> Hi Shankara,
>>>
>>> Looks bad. Can you provide a reproducer?
>>> We extensively use kcov with syzkaller, but have not observed such
>>> leaks. Also I don't see anything obvious in the code.
>>>
>>> Thanks
>>

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Dmitry Vyukov]

On Sat, Jan 20, 2018 at 4:01 PM, Shankara Pailoor  wrote:
> Hi Dmitry,
>
> I will try and get something to you tomorrow. Just wondering, but what
> happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
> twice? I am looking here
> https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
> and I don't see where the previous struct would get freed.

Good question. Perhaps we need something like:

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 7594c033d98a..c76498018500 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -358,7 +358,7 @@ static int kcov_ioctl_locked(struct kcov *kcov,
unsigned int cmd,
 */
if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
return -EINVAL;
-   if (kcov->t != NULL)
+   if (kcov->t != NULL || t->kcov != NULL)
return -EBUSY;
if (arg == KCOV_TRACE_PC)
kcov->mode = KCOV_MODE_TRACE_PC;



> On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov  wrote:
>> On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  
>> wrote:
>>> Hi Dmitry,
>>>
>>> I added support for kcov in strace and I have been tracing a fairly
>>> large program but after a little while, I notice that when I mmap a
>>> new cover buffer, the call fails with ENOMEM. After killing the
>>> program, I try and rerun and I notice that there is nearly no memory
>>> on the system. When I do a kmemleak scan I get the following reports:
>>>
>>> I believe the problem occurs when I try and setup the kcov buffer
>>> again after an exec. Instead of reusing the old file descriptor I open
>>> kcov again within that process. In that case, I don't know what
>>> happens to the old kcov struct.
>>>
>>> I don't see a maintainers list for kcov so I decided to email you
>>> directly. Let me know what more information I can provide.
>>
>>
>> Hi Shankara,
>>
>> Looks bad. Can you provide a reproducer?
>> We extensively use kcov with syzkaller, but have not observed such
>> leaks. Also I don't see anything obvious in the code.
>>
>> Thanks
>

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Dmitry Vyukov]

On Sat, Jan 20, 2018 at 4:01 PM, Shankara Pailoor  wrote:
> Hi Dmitry,
>
> I will try and get something to you tomorrow. Just wondering, but what
> happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
> twice? I am looking here
> https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
> and I don't see where the previous struct would get freed.

Good question. Perhaps we need something like:

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 7594c033d98a..c76498018500 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -358,7 +358,7 @@ static int kcov_ioctl_locked(struct kcov *kcov,
unsigned int cmd,
 */
if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
return -EINVAL;
-   if (kcov->t != NULL)
+   if (kcov->t != NULL || t->kcov != NULL)
return -EBUSY;
if (arg == KCOV_TRACE_PC)
kcov->mode = KCOV_MODE_TRACE_PC;



> On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov  wrote:
>> On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  
>> wrote:
>>> Hi Dmitry,
>>>
>>> I added support for kcov in strace and I have been tracing a fairly
>>> large program but after a little while, I notice that when I mmap a
>>> new cover buffer, the call fails with ENOMEM. After killing the
>>> program, I try and rerun and I notice that there is nearly no memory
>>> on the system. When I do a kmemleak scan I get the following reports:
>>>
>>> I believe the problem occurs when I try and setup the kcov buffer
>>> again after an exec. Instead of reusing the old file descriptor I open
>>> kcov again within that process. In that case, I don't know what
>>> happens to the old kcov struct.
>>>
>>> I don't see a maintainers list for kcov so I decided to email you
>>> directly. Let me know what more information I can provide.
>>
>>
>> Hi Shankara,
>>
>> Looks bad. Can you provide a reproducer?
>> We extensively use kcov with syzkaller, but have not observed such
>> leaks. Also I don't see anything obvious in the code.
>>
>> Thanks
>

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Shankara Pailoor]

Hi Dmitry,

I will try and get something to you tomorrow. Just wondering, but what
happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
twice? I am looking here
https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
and I don't see where the previous struct would get freed.

Regards,
Shankara

On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov  wrote:
> On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  wrote:
>> Hi Dmitry,
>>
>> I added support for kcov in strace and I have been tracing a fairly
>> large program but after a little while, I notice that when I mmap a
>> new cover buffer, the call fails with ENOMEM. After killing the
>> program, I try and rerun and I notice that there is nearly no memory
>> on the system. When I do a kmemleak scan I get the following reports:
>>
>> I believe the problem occurs when I try and setup the kcov buffer
>> again after an exec. Instead of reusing the old file descriptor I open
>> kcov again within that process. In that case, I don't know what
>> happens to the old kcov struct.
>>
>> I don't see a maintainers list for kcov so I decided to email you
>> directly. Let me know what more information I can provide.
>
>
> Hi Shankara,
>
> Looks bad. Can you provide a reproducer?
> We extensively use kcov with syzkaller, but have not observed such
> leaks. Also I don't see anything obvious in the code.
>
> Thanks

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Shankara Pailoor]

Hi Dmitry,

I will try and get something to you tomorrow. Just wondering, but what
happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
twice? I am looking here
https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
and I don't see where the previous struct would get freed.

Regards,
Shankara

On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov  wrote:
> On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  wrote:
>> Hi Dmitry,
>>
>> I added support for kcov in strace and I have been tracing a fairly
>> large program but after a little while, I notice that when I mmap a
>> new cover buffer, the call fails with ENOMEM. After killing the
>> program, I try and rerun and I notice that there is nearly no memory
>> on the system. When I do a kmemleak scan I get the following reports:
>>
>> I believe the problem occurs when I try and setup the kcov buffer
>> again after an exec. Instead of reusing the old file descriptor I open
>> kcov again within that process. In that case, I don't know what
>> happens to the old kcov struct.
>>
>> I don't see a maintainers list for kcov so I decided to email you
>> directly. Let me know what more information I can provide.
>
>
> Hi Shankara,
>
> Looks bad. Can you provide a reproducer?
> We extensively use kcov with syzkaller, but have not observed such
> leaks. Also I don't see anything obvious in the code.
>
> Thanks

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Dmitry Vyukov]

On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  wrote:
> Hi Dmitry,
>
> I added support for kcov in strace and I have been tracing a fairly
> large program but after a little while, I notice that when I mmap a
> new cover buffer, the call fails with ENOMEM. After killing the
> program, I try and rerun and I notice that there is nearly no memory
> on the system. When I do a kmemleak scan I get the following reports:
>
> I believe the problem occurs when I try and setup the kcov buffer
> again after an exec. Instead of reusing the old file descriptor I open
> kcov again within that process. In that case, I don't know what
> happens to the old kcov struct.
>
> I don't see a maintainers list for kcov so I decided to email you
> directly. Let me know what more information I can provide.


Hi Shankara,

Looks bad. Can you provide a reproducer?
We extensively use kcov with syzkaller, but have not observed such
leaks. Also I don't see anything obvious in the code.

Thanks

Re: Possible Memory Leak in KCOV Linux 4.15-rc1

[Dmitry Vyukov]

On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor  wrote:
> Hi Dmitry,
>
> I added support for kcov in strace and I have been tracing a fairly
> large program but after a little while, I notice that when I mmap a
> new cover buffer, the call fails with ENOMEM. After killing the
> program, I try and rerun and I notice that there is nearly no memory
> on the system. When I do a kmemleak scan I get the following reports:
>
> I believe the problem occurs when I try and setup the kcov buffer
> again after an exec. Instead of reusing the old file descriptor I open
> kcov again within that process. In that case, I don't know what
> happens to the old kcov struct.
>
> I don't see a maintainers list for kcov so I decided to email you
> directly. Let me know what more information I can provide.


Hi Shankara,

Looks bad. Can you provide a reproducer?
We extensively use kcov with syzkaller, but have not observed such
leaks. Also I don't see anything obvious in the code.

Thanks