Re: [libnetfilter_log] fix bug in race condition of calling nflog_open from different threads at same time

[Phil Sutter <phil@nwl.cc>]

Evgen,

On Tue, Apr 30, 2024 at 01:18:29PM +0300, Evgen Bendyak wrote:
> This patch addresses a bug that occurs when the nflog_open function is
> called concurrently from different threads within an application. The
> function nflog_open internally invokes nflog_open_nfnl. Within this
> function, a static global variable pkt_cb (static struct nfnl_callback
> pkt_cb) is used. This variable is assigned a pointer to a newly
> created structure (pkt_cb.data = h;) and is passed to
> nfnl_callback_register. The issue arises with concurrent execution of
> pkt_cb.data = h;, as only one of the simultaneously created
> nflog_handle structures is retained due to the callback function.
> Subsequently, the callback function __nflog_rcv_pkt is invoked for all
> the nflog_open structures, but only references one of them.
> Consequently, the callbacks registered by the end-user of the library
> through nflog_callback_register fail to trigger in sessions where the
> incorrect reference was recorded.
> This patch corrects this behavior by creating the structure locally on
> the stack for each call to nflog_open_nfnl. Since the
> nfnl_callback_register function simply copies the data into its
> internal structures, there is no need to retain pkt_cb beyond this
> point.

Patch looks sane, but I fear formatting won't do. Are you able to turn
this into a git commit and use git-format-patch/git-send-email to submit
it?

Thanks, Phil