Hi,
Le 06/04/2022 à 23:59, Stephen Hemminger a écrit :
On Wed, 6 Apr 2022 12:22:13 +0200
Yann Droneaud <ydroneaud@xxxxxxxxxx> wrote:
Abstract unix socket address are bytes sequences up to
108 bytes (UNIX_PATH_MAX == sizeof(struct sockaddr_un) -
offsetof(struct sockaddr_un, sun_path)).
As with any random string of bytes, printing them in
/proc/net/unix should be done with caution to prevent
misbehavior.
It would have been great to use seq_escape_mem() to escape
the control characters in a reversible way.
Unfortunately userspace might expect that NUL bytes are
replaced with '@' characters as it's done currently.
So this patch implements the following scheme: any control
characters, including NUL, in the abstract unix socket
addresses is replaced by '@' characters.
Sadly, with such non reversible escape scheme, abstract
addresses such as "\0\0", "\0\a", "\0\b", "\0\t", etc.
will have the same representation: "@@".
But will prevent "cat /proc/net/unix" from messing with
terminal, and will prevent "\n" in abstract address from
messing with parsing the list of Unix sockets.
Signed-off-by: Yann Droneaud <ydroneaud@xxxxxxxxxx>
---
net/unix/af_unix.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e71a312faa1e..8021efd92301 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -3340,7 +3340,8 @@ static int unix_seq_show(struct seq_file *seq, void *v)
i++;
}
for ( ; i < len; i++)
- seq_putc(seq, u->addr->name->sun_path[i] ?:
+ seq_putc(seq, !iscntrl(u->addr->name->sun_path[i]) ?
+ u->addr->name->sun_path[i] :
'@');
}
unix_state_unlock(s);
Unfortunately, you will break userspace ABI with this.
It's a wanted side effect.
Consider the following program
#include <stddef.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>
#define ADDRESS "\0\n0000000000000000: 00000003 00000000 00000000 0001 03 1234567890 /bin/true"
int main(void)
{
static const struct sockaddr_un un = {
.sun_family = AF_UNIX,
.sun_path = ADDRESS,
};
int s;
s = socket(AF_UNIX, SOCK_STREAM, 0);
if (s < 0) {
perror("socket");
return 1;
}
if (bind(s, (const struct sockaddr *)&un, offsetof(struct sockaddr_un,sun_path) + sizeof(ADDRESS) - 1) < 0) {
perror("bind");
return 1;
}
while (1)
pause();
return 0;
}
This confuses
- cat /proc/net/unix
- netstat -x
Only ss -xl doesn't take /bin/true as a Unix socket (but ss output is broken because it doesn't escape \n in unix addresses)
Regards.
--
Yann Droneaud
OPTEYA
