diff mbox series

[net,v2] net: fix pos incrementment in ipv6_route_seq_next

Message ID 20201013183121.1988411-1-yhs@fb.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series [net,v2] net: fix pos incrementment in ipv6_route_seq_next | expand

Commit Message

Yonghong Song Oct. 13, 2020, 6:31 p.m. UTC 
Commit 4fc427e05158 ("ipv6_route_seq_next should increase position index")
tried to fix the issue where seq_file pos is not increased
if a NULL element is returned with seq_ops->next(). See bug
  https://bugzilla.kernel.org/show_bug.cgi?id=206283
The commit effectively does:
  - increase pos for all seq_ops->start()
  - increase pos for all seq_ops->next()

For ipv6_route, increasing pos for all seq_ops->next() is correct.
But increasing pos for seq_ops->start() is not correct
since pos is used to determine how many items to skip during
seq_ops->start():
  iter->skip = *pos;
seq_ops->start() just fetches the *current* pos item.
The item can be skipped only after seq_ops->show() which essentially
is the beginning of seq_ops->next().

For example, I have 7 ipv6 route entries,
  root@arch-fb-vm1:~/net-next dd if=/proc/net/ipv6_route bs=4096
  00000000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000400 00000001 00000000 00000001     eth0
  fe800000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000001 00000000 00000001     eth0
  00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
  00000000000000000000000000000001 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000003 00000000 80200001       lo
  fe800000000000002050e3fffebd3be8 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80200001     eth0
  ff000000000000000000000000000000 08 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000004 00000000 00000001     eth0
  00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
  0+1 records in
  0+1 records out
  1050 bytes (1.0 kB, 1.0 KiB) copied, 0.00707908 s, 148 kB/s
  root@arch-fb-vm1:~/net-next

In the above, I specify buffer size 4096, so all records can be returned
to user space with a single trip to the kernel.

If I use buffer size 128, since each record size is 149, internally
kernel seq_read() will read 149 into its internal buffer and return the data
to user space in two read() syscalls. Then user read() syscall will trigger
next seq_ops->start(). Since the current implementation increased pos even
for seq_ops->start(), it will skip record #2, #4 and #6, assuming the first
record is #1.

  root@arch-fb-vm1:~/net-next dd if=/proc/net/ipv6_route bs=128
  00000000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000400 00000001 00000000 00000001     eth0
  00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
  fe800000000000002050e3fffebd3be8 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80200001     eth0
  00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
4+1 records in
4+1 records out
600 bytes copied, 0.00127758 s, 470 kB/s

To fix the problem, create a fake pos pointer so seq_ops->start()
won't actually increase seq_file pos. With this fix, the
above `dd` command with `bs=128` will show correct result.

Fixes: 4fc427e05158 ("ipv6_route_seq_next should increase position index")
Cc: Vasily Averin <vvs@virtuozzo.com>
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Suggested-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 net/ipv6/ip6_fib.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Changelog:
 v1 -> v2:
  - instead of push increment of *pos in ipv6_route_seq_next() for
    seq_ops->next() only. Add a face pos pointer in seq_ops->start()
    and use it when calling ipv6_route_seq_next().

Comments

Vasily Averin Oct. 14, 2020, 4:34 a.m. UTC | #1 
On 10/13/20 9:31 PM, Yonghong Song wrote:
> Commit 4fc427e05158 ("ipv6_route_seq_next should increase position index")
> tried to fix the issue where seq_file pos is not increased
> if a NULL element is returned with seq_ops->next(). See bug
>   https://bugzilla.kernel.org/show_bug.cgi?id=206283
> The commit effectively does:
>   - increase pos for all seq_ops->start()
>   - increase pos for all seq_ops->next()
> 
> For ipv6_route, increasing pos for all seq_ops->next() is correct.
> But increasing pos for seq_ops->start() is not correct
> since pos is used to determine how many items to skip during
> seq_ops->start():
>   iter->skip = *pos;
> seq_ops->start() just fetches the *current* pos item.
> The item can be skipped only after seq_ops->show() which essentially
> is the beginning of seq_ops->next().
> 
> For example, I have 7 ipv6 route entries,
>   root@arch-fb-vm1:~/net-next dd if=/proc/net/ipv6_route bs=4096
>   00000000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000400 00000001 00000000 00000001     eth0
>   fe800000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000001 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   00000000000000000000000000000001 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000003 00000000 80200001       lo
>   fe800000000000002050e3fffebd3be8 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80200001     eth0
>   ff000000000000000000000000000000 08 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000004 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   0+1 records in
>   0+1 records out
>   1050 bytes (1.0 kB, 1.0 KiB) copied, 0.00707908 s, 148 kB/s
>   root@arch-fb-vm1:~/net-next
> 
> In the above, I specify buffer size 4096, so all records can be returned
> to user space with a single trip to the kernel.
> 
> If I use buffer size 128, since each record size is 149, internally
> kernel seq_read() will read 149 into its internal buffer and return the data
> to user space in two read() syscalls. Then user read() syscall will trigger
> next seq_ops->start(). Since the current implementation increased pos even
> for seq_ops->start(), it will skip record #2, #4 and #6, assuming the first
> record is #1.
> 
>   root@arch-fb-vm1:~/net-next dd if=/proc/net/ipv6_route bs=128
>   00000000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000400 00000001 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   fe800000000000002050e3fffebd3be8 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80200001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
> 4+1 records in
> 4+1 records out
> 600 bytes copied, 0.00127758 s, 470 kB/s
> 
> To fix the problem, create a fake pos pointer so seq_ops->start()
> won't actually increase seq_file pos. With this fix, the
> above `dd` command with `bs=128` will show correct result.
> 
> Fixes: 4fc427e05158 ("ipv6_route_seq_next should increase position index")
> Cc: Vasily Averin <vvs@virtuozzo.com>
> Cc: Andrii Nakryiko <andriin@fb.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Suggested-by: Vasily Averin <vvs@virtuozzo.com>
> Signed-off-by: Yonghong Song <yhs@fb.com>
Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
> ---
>  net/ipv6/ip6_fib.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Changelog:
>  v1 -> v2:
>   - instead of push increment of *pos in ipv6_route_seq_next() for
>     seq_ops->next() only. Add a face pos pointer in seq_ops->start()
>     and use it when calling ipv6_route_seq_next().
> 
> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index 141c0a4c569a..e633b2b7deda 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -2622,8 +2622,10 @@ static void *ipv6_route_seq_start(struct seq_file *seq, loff_t *pos)
>  	iter->skip = *pos;
>  
>  	if (iter->tbl) {
> +		loff_t p;
> +
>  		ipv6_route_seq_setup_walk(iter, net);
> -		return ipv6_route_seq_next(seq, NULL, pos);
> +		return ipv6_route_seq_next(seq, NULL, &p);
>  	} else {
>  		return NULL;
>  	}
>
Eric Dumazet Oct. 14, 2020, 8:10 a.m. UTC | #2 
On 10/13/20 8:31 PM, Yonghong Song wrote:
> Commit 4fc427e05158 ("ipv6_route_seq_next should increase position index")
> tried to fix the issue where seq_file pos is not increased
> if a NULL element is returned with seq_ops->next(). See bug
>   https://bugzilla.kernel.org/show_bug.cgi?id=206283
> The commit effectively does:
>   - increase pos for all seq_ops->start()
>   - increase pos for all seq_ops->next()
> 
> For ipv6_route, increasing pos for all seq_ops->next() is correct.
> But increasing pos for seq_ops->start() is not correct
> since pos is used to determine how many items to skip during
> seq_ops->start():
>   iter->skip = *pos;
> seq_ops->start() just fetches the *current* pos item.
> The item can be skipped only after seq_ops->show() which essentially
> is the beginning of seq_ops->next().
> 
> For example, I have 7 ipv6 route entries,
>   root@arch-fb-vm1:~/net-next dd if=/proc/net/ipv6_route bs=4096
>   00000000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000400 00000001 00000000 00000001     eth0
>   fe800000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000001 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   00000000000000000000000000000001 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000003 00000000 80200001       lo
>   fe800000000000002050e3fffebd3be8 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80200001     eth0
>   ff000000000000000000000000000000 08 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000004 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   0+1 records in
>   0+1 records out
>   1050 bytes (1.0 kB, 1.0 KiB) copied, 0.00707908 s, 148 kB/s
>   root@arch-fb-vm1:~/net-next
> 
> In the above, I specify buffer size 4096, so all records can be returned
> to user space with a single trip to the kernel.
> 
> If I use buffer size 128, since each record size is 149, internally
> kernel seq_read() will read 149 into its internal buffer and return the data
> to user space in two read() syscalls. Then user read() syscall will trigger
> next seq_ops->start(). Since the current implementation increased pos even
> for seq_ops->start(), it will skip record #2, #4 and #6, assuming the first
> record is #1.
> 
>   root@arch-fb-vm1:~/net-next dd if=/proc/net/ipv6_route bs=128
>   00000000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000400 00000001 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   fe800000000000002050e3fffebd3be8 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80200001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
> 4+1 records in
> 4+1 records out
> 600 bytes copied, 0.00127758 s, 470 kB/s
> 
> To fix the problem, create a fake pos pointer so seq_ops->start()
> won't actually increase seq_file pos. With this fix, the
> above `dd` command with `bs=128` will show correct result.
> 
> Fixes: 4fc427e05158 ("ipv6_route_seq_next should increase position index")
> Cc: Vasily Averin <vvs@virtuozzo.com>
> Cc: Andrii Nakryiko <andriin@fb.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Suggested-by: Vasily Averin <vvs@virtuozzo.com>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
>  net/ipv6/ip6_fib.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Changelog:
>  v1 -> v2:
>   - instead of push increment of *pos in ipv6_route_seq_next() for
>     seq_ops->next() only. Add a face pos pointer in seq_ops->start()
>     and use it when calling ipv6_route_seq_next().
> 
> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index 141c0a4c569a..e633b2b7deda 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -2622,8 +2622,10 @@ static void *ipv6_route_seq_start(struct seq_file *seq, loff_t *pos)
>  	iter->skip = *pos;
>  
>  	if (iter->tbl) {
> +		loff_t p;

Please init this, otherwise I can guarantee syzbot will be not happy.

                p = *pos;

> +
>  		ipv6_route_seq_setup_walk(iter, net);
> -		return ipv6_route_seq_next(seq, NULL, pos);
> +		return ipv6_route_seq_next(seq, NULL, &p);
>  	} else {
>  		return NULL;
>  	}
>
diff mbox series

Patch

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 141c0a4c569a..e633b2b7deda 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -2622,8 +2622,10 @@  static void *ipv6_route_seq_start(struct seq_file *seq, loff_t *pos)
 	iter->skip = *pos;
 
 	if (iter->tbl) {
+		loff_t p;
+
 		ipv6_route_seq_setup_walk(iter, net);
-		return ipv6_route_seq_next(seq, NULL, pos);
+		return ipv6_route_seq_next(seq, NULL, &p);
 	} else {
 		return NULL;
 	}