Re: [PATCH] net: check net.core.somaxconn sysctl values

On Wed, 2013-07-31 at 17:57 +0400, Roman Gushchin wrote:

It's possible to assign an invalid value to the net.core.somaxconn
sysctl variable, because there is no checks at all.

The sk_max_ack_backlog field of the sock structure is defined as
unsigned short. Therefore, the backlog argument in inet_listen()
shouldn't exceed USHRT_MAX. The backlog argument in the listen() syscall
is truncated to the somaxconn value. So, the somaxconn value shouldn't
exceed 65535 (USHRT_MAX).
Also, negative values of somaxconn are meaningless.

before:
$ sysctl -w net.core.somaxconn=256
net.core.somaxconn = 256
$ sysctl -w net.core.somaxconn=65536
net.core.somaxconn = 65536
$ sysctl -w net.core.somaxconn=-100
net.core.somaxconn = -100

after:
$ sysctl -w net.core.somaxconn=256
net.core.somaxconn = 256
$ sysctl -w net.core.somaxconn=65536
error: "Invalid argument" setting key "net.core.somaxconn"
$ sysctl -w net.core.somaxconn=-100
error: "Invalid argument" setting key "net.core.somaxconn"

Signed-off-by: Roman Gushchin <redacted>
---
  net/core/sysctl_net_core.c | 6 +++++-
  1 file changed, 5 insertions(+), 1 deletion(-)

We had a discussion about this one month ago, as Changli Gao posted a
patch. http://patchwork.ozlabs.org/patch/255460/

So proper credits would be nice ;)

Based on a prior patch from Changli Gao

Reported-by: Changli Gao <redacted>
Suggested-by: Eric Dumazet <edumazet@google.com>

Acked-by: Eric Dumazet <edumazet@google.com>