[PATCH] relayfs: fix out-of-bounds access in relay_file_read

[PATCH] relayfs: fix out-of-bounds access in relay_file_read

[zhangzhengming]

From: Zhang Zhengming <zhang.zhengming@h3c.com>

There is a crash in relay_file_read, as the var from 
point to the end of last subbuf.
The oops looks something like:
pc : __arch_copy_to_user+0x180/0x310
lr : relay_file_read+0x20c/0x2c8
Call trace:
 __arch_copy_to_user+0x180/0x310
 full_proxy_read+0x68/0x98
 vfs_read+0xb0/0x1d0
 ksys_read+0x6c/0xf0
 __arm64_sys_read+0x20/0x28
 el0_svc_common.constprop.3+0x84/0x108
 do_el0_svc+0x74/0x90
 el0_svc+0x1c/0x28
 el0_sync_handler+0x88/0xb0
 el0_sync+0x148/0x180

We get the condition by analyzing the vmcore:
1). The last produced byte and last consumed byte
    both at the end of the last subbuf
2). A softirq who will call function(e.g __blk_add_trace)
    to write relay buffer occurs when an program calling
    function relay_file_read_avail.
        relay_file_read
                relay_file_read_avail
                        relay_file_read_consume(buf, 0, 0);
                        //interrupted by softirq who will write subbuf
                        ....
                        return 1;
                //read_start point to the end of the last subbuf
                read_start = relay_file_read_start_pos
                //avail is equal to subsize
                avail = relay_file_read_subbuf_avail
                //from  points to an invalid memory address             
                from = buf->start + read_start
                //system is crashed
                copy_to_user(buffer, from, avail)

Signed-off-by: Zhang Zhengming <zhang.zhengming@h3c.com>
Reviewed-by: Zhao Lei <zhao_lei1@hoperun.com>
Reviewed-by: Zhou Kete <zhou.kete@h3c.com>
---
 kernel/relay.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/relay.c b/kernel/relay.c
index 9aa70ae..a80fa01 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -989,7 +989,8 @@ static size_t relay_file_read_start_pos(struct rchan_buf *buf)
 	size_t subbuf_size = buf->chan->subbuf_size;
 	size_t n_subbufs = buf->chan->n_subbufs;
 	size_t consumed = buf->subbufs_consumed % n_subbufs;
-	size_t read_pos = consumed * subbuf_size + buf->bytes_consumed;
+	size_t read_pos = (consumed * subbuf_size + buf->bytes_consumed)
+			% (n_subbufs * subbuf_size);
 
 	read_subbuf = read_pos / subbuf_size;
 	padding = buf->padding[read_subbuf];
-- 
2.17.1

Re: [PATCH] relayfs: fix out-of-bounds access in relay_file_read

[Andrew Morton]

On Wed, 19 Apr 2023 12:02:03 +0800 zhangzhengming <zhang.zhengming@h3c.com> wrote:

> From: Zhang Zhengming <zhang.zhengming@h3c.com>
> 
> There is a crash in relay_file_read, as the var from 
> point to the end of last subbuf.
> The oops looks something like:
> pc : __arch_copy_to_user+0x180/0x310
> lr : relay_file_read+0x20c/0x2c8
> Call trace:
>  __arch_copy_to_user+0x180/0x310
>  full_proxy_read+0x68/0x98
>  vfs_read+0xb0/0x1d0
>  ksys_read+0x6c/0xf0
>  __arm64_sys_read+0x20/0x28
>  el0_svc_common.constprop.3+0x84/0x108
>  do_el0_svc+0x74/0x90
>  el0_svc+0x1c/0x28
>  el0_sync_handler+0x88/0xb0
>  el0_sync+0x148/0x180
> 
> We get the condition by analyzing the vmcore:
> 1). The last produced byte and last consumed byte
>     both at the end of the last subbuf
> 2). A softirq who will call function(e.g __blk_add_trace)
>     to write relay buffer occurs when an program calling
>     function relay_file_read_avail.
>         relay_file_read
>                 relay_file_read_avail
>                         relay_file_read_consume(buf, 0, 0);
>                         //interrupted by softirq who will write subbuf
>                         ....
>                         return 1;
>                 //read_start point to the end of the last subbuf
>                 read_start = relay_file_read_start_pos
>                 //avail is equal to subsize
>                 avail = relay_file_read_subbuf_avail
>                 //from  points to an invalid memory address             
>                 from = buf->start + read_start
>                 //system is crashed
>                 copy_to_user(buffer, from, avail)

Thanks.  Hopefully Pengcheng Yang and Jens Axboe can comment.

> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -989,7 +989,8 @@ static size_t relay_file_read_start_pos(struct rchan_buf *buf)
>  	size_t subbuf_size = buf->chan->subbuf_size;
>  	size_t n_subbufs = buf->chan->n_subbufs;
>  	size_t consumed = buf->subbufs_consumed % n_subbufs;
> -	size_t read_pos = consumed * subbuf_size + buf->bytes_consumed;
> +	size_t read_pos = (consumed * subbuf_size + buf->bytes_consumed)
> +			% (n_subbufs * subbuf_size);
>  
>  	read_subbuf = read_pos / subbuf_size;
>  	padding = buf->padding[read_subbuf];

I'm thinking we should backport this into earlier kernels and that the
commit we're fixing is

Fixes: 341a7213e5c1 ("kernel/relay.c: fix read_pos error when multiple readers")

Re: [PATCH] relayfs: fix out-of-bounds access in relay_file_read

[Jens Axboe]

On 4/19/23 3:03?PM, Andrew Morton wrote:
> On Wed, 19 Apr 2023 12:02:03 +0800 zhangzhengming <zhang.zhengming@h3c.com> wrote:
> 
>> From: Zhang Zhengming <zhang.zhengming@h3c.com>
>>
>> There is a crash in relay_file_read, as the var from 
>> point to the end of last subbuf.
>> The oops looks something like:
>> pc : __arch_copy_to_user+0x180/0x310
>> lr : relay_file_read+0x20c/0x2c8
>> Call trace:
>>  __arch_copy_to_user+0x180/0x310
>>  full_proxy_read+0x68/0x98
>>  vfs_read+0xb0/0x1d0
>>  ksys_read+0x6c/0xf0
>>  __arm64_sys_read+0x20/0x28
>>  el0_svc_common.constprop.3+0x84/0x108
>>  do_el0_svc+0x74/0x90
>>  el0_svc+0x1c/0x28
>>  el0_sync_handler+0x88/0xb0
>>  el0_sync+0x148/0x180
>>
>> We get the condition by analyzing the vmcore:
>> 1). The last produced byte and last consumed byte
>>     both at the end of the last subbuf
>> 2). A softirq who will call function(e.g __blk_add_trace)
>>     to write relay buffer occurs when an program calling
>>     function relay_file_read_avail.
>>         relay_file_read
>>                 relay_file_read_avail
>>                         relay_file_read_consume(buf, 0, 0);
>>                         //interrupted by softirq who will write subbuf
>>                         ....
>>                         return 1;
>>                 //read_start point to the end of the last subbuf
>>                 read_start = relay_file_read_start_pos
>>                 //avail is equal to subsize
>>                 avail = relay_file_read_subbuf_avail
>>                 //from  points to an invalid memory address             
>>                 from = buf->start + read_start
>>                 //system is crashed
>>                 copy_to_user(buffer, from, avail)
> 
> Thanks.  Hopefully Pengcheng Yang and Jens Axboe can comment.

Patch looks good to me, but that doesn't necessarily say much. I never
did much relayfs hacking, and the bits I did was probably almost 20
years ago at this point when I wrote blktrace...

-- 
Jens Axboe

Re: [PATCH] relayfs: fix out-of-bounds access in relay_file_read

[Pengcheng Yang]

On April 20, 2023 5:04 AM, Andrew Morton wrote:
> On Wed, 19 Apr 2023 12:02:03 +0800 zhangzhengming <zhang.zhengming@h3c.com> wrote:
>
>> From: Zhang Zhengming <zhang.zhengming@h3c.com>
>> 
>> There is a crash in relay_file_read, as the var from 
>> point to the end of last subbuf.
>> The oops looks something like:
>> pc : __arch_copy_to_user+0x180/0x310
>> lr : relay_file_read+0x20c/0x2c8
>> Call trace:
>>  __arch_copy_to_user+0x180/0x310
>>  full_proxy_read+0x68/0x98
>>  vfs_read+0xb0/0x1d0
>>  ksys_read+0x6c/0xf0
>>  __arm64_sys_read+0x20/0x28
>>  el0_svc_common.constprop.3+0x84/0x108
>>  do_el0_svc+0x74/0x90
>>  el0_svc+0x1c/0x28
>>  el0_sync_handler+0x88/0xb0
>>  el0_sync+0x148/0x180
>> 
>> We get the condition by analyzing the vmcore:
>> 1). The last produced byte and last consumed byte
>>     both at the end of the last subbuf
>> 2). A softirq who will call function(e.g __blk_add_trace)
>>     to write relay buffer occurs when an program calling
>>     function relay_file_read_avail.
>>         relay_file_read
>>                 relay_file_read_avail
>>                         relay_file_read_consume(buf, 0, 0);
>>                         //interrupted by softirq who will write subbuf
>>                         ....
>>                         return 1;
>>                 //read_start point to the end of the last subbuf
>>                 read_start = relay_file_read_start_pos
>>                 //avail is equal to subsize
>>                 avail = relay_file_read_subbuf_avail
>>                 //from  points to an invalid memory address             
>>                 from = buf->start + read_start
>>                 //system is crashed
>>                 copy_to_user(buffer, from, avail)
>
> Thanks.  Hopefully Pengcheng Yang and Jens Axboe can comment.

This patch looks good to me.

Reviewed-by: Pengcheng Yang <yangpc@wangsu.com>

>
> I'm thinking we should backport this into earlier kernels and that the
> commit we're fixing is
>
> Fixes: 341a7213e5c1 ("kernel/relay.c: fix read_pos error when multiple readers")

I suggest starting backport with this tag:

Fixes: 8d62fdebdaf9 ("relay file read: start-pos fix")