Re: [PATCH] arp, tap, util: Don't use perror() after seccomp filter is installed

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Nov 15, 2022 at 02:24:00AM +0100, Stefano Brivio wrote:
> If stderr is closed, after we fork to background, glibc's
> implementation of perror() will try to re-open it by calling dup(),
> upon which the seccomp filter causes the process to terminate,
> because dup() is not included in the list of allowed syscalls.
> 
> Replace perror() calls that might happen after isolation_postfork().
> We could probably replace all of them, but early ones need a bit more
> attention as we have to check whether log.c functions work in early
> stages.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  arp.c  | 6 ++++--
>  tap.c  | 6 +++---
>  util.c | 6 +++---
>  3 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/arp.c b/arp.c
> index 141d43f..930b9ea 100644
> --- a/arp.c
> +++ b/arp.c
> @@ -24,6 +24,7 @@
>  #include <string.h>
>  
>  #include "util.h"
> +#include "log.h"
>  #include "arp.h"
>  #include "dhcp.h"
>  #include "passt.h"
> @@ -43,6 +44,7 @@ int arp(const struct ctx *c, const struct pool *p)
>  	struct arphdr *ah;
>  	struct arpmsg *am;
>  	size_t len;
> +	int ret;
>  
>  	eh = packet_get(p, 0, 0,			 sizeof(*eh), NULL);
>  	ah = packet_get(p, 0, sizeof(*eh),		 sizeof(*ah), NULL);
> @@ -81,8 +83,8 @@ int arp(const struct ctx *c, const struct pool *p)
>  	memcpy(eh->h_dest,	eh->h_source,	sizeof(eh->h_dest));
>  	memcpy(eh->h_source,	c->mac,		sizeof(eh->h_source));
>  
> -	if (tap_send(c, eh, len) < 0)
> -		perror("ARP: send");
> +	if ((ret = tap_send(c, eh, len)) < 0)
> +		warn("ARP: send: %s", strerror(ret));
>  
>  	return 1;
>  }
> diff --git a/tap.c b/tap.c
> index abeff25..b7ac996 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -899,7 +899,7 @@ static void tap_sock_unix_init(struct ctx *c)
>  	int i;
>  
>  	if (fd < 0) {
> -		perror("UNIX socket");
> +		err("UNIX socket: %s", strerror(errno));
>  		exit(EXIT_FAILURE);
>  	}
>  
> @@ -920,7 +920,7 @@ static void tap_sock_unix_init(struct ctx *c)
>  
>  		ex = socket(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK, 0);
>  		if (ex < 0) {
> -			perror("UNIX domain socket check");
> +			err("UNIX domain socket check: %s", strerror(errno));
>  			exit(EXIT_FAILURE);
>  		}
>  
> @@ -944,7 +944,7 @@ static void tap_sock_unix_init(struct ctx *c)
>  	}
>  
>  	if (i == UNIX_SOCK_MAX) {
> -		perror("UNIX socket bind");
> +		err("UNIX socket bind: %s", strerror(errno));
>  		exit(EXIT_FAILURE);
>  	}
>  
> diff --git a/util.c b/util.c
> index 514bd44..be102e3 100644
> --- a/util.c
> +++ b/util.c
> @@ -125,7 +125,7 @@ int sock_l4(const struct ctx *c, int af, uint8_t proto,
>  		fd = socket(af, SOCK_DGRAM | SOCK_NONBLOCK, proto);
>  
>  	if (fd < 0) {
> -		perror("L4 socket");
> +		warn("L4 socket: %s", strerror(errno));
>  		return -1;
>  	}
>  
> @@ -193,7 +193,7 @@ int sock_l4(const struct ctx *c, int af, uint8_t proto,
>  	}
>  
>  	if (proto == IPPROTO_TCP && listen(fd, 128) < 0) {
> -		perror("TCP socket listen");
> +		warn("TCP socket listen: %s", strerror(errno));
>  		close(fd);
>  		return -1;
>  	}
> @@ -201,7 +201,7 @@ int sock_l4(const struct ctx *c, int af, uint8_t proto,
>  	ev.events = EPOLLIN;
>  	ev.data.u64 = ref.u64;
>  	if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
> -		perror("L4 epoll_ctl");
> +		warn("L4 epoll_ctl: %s", strerror(errno));
>  		return -1;
>  	}
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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