* [RFC] apparently bogus logics in unix_find_other() since 2002
@ 2019-02-10 4:24 Al Viro
2019-02-11 3:19 ` Al Viro
2019-02-11 11:21 ` Solar Designer
0 siblings, 2 replies; 3+ messages in thread
From: Al Viro @ 2019-02-10 4:24 UTC (permalink / raw)
To: netdev; +Cc: Solar Designer, David Miller
In "net/unix/af_unix.c: Set ATIME on socket inode" (back in
2002) we'd grown something rather odd in unix_find_other(). In the
original patch it was
u=unix_find_socket_byname(sunname, len, type, hash);
- if (!u)
+ if (u) {
+ struct dentry *dentry;
+ dentry = u->protinfo.af_unix.dentry;
+ if (dentry)
+ UPDATE_ATIME(dentry->d_inode);
+ } else
goto fail;
These days the code is
u = unix_find_socket_byname(net, sunname, len, type, hash);
if (u) {
struct dentry *dentry;
dentry = unix_sk(u)->path.dentry;
if (dentry)
touch_atime(&unix_sk(u)->path);
} else
goto fail;
but the logics is the same. It's the abstract address case - we have
'\0' in sunname->sun_path[0]. How in hell could that possibly have
non-NULL ->path.dentry and what would it be?
Note that unix_find_socket_byname() returns non-NULL u here only if
u->addr->name->sun_path[0] is equal to sunname->sun_path[0], i.e.
'\0'. There are only two places where we ever might assign non-NULL
to ->path.dentry:
if (sun_path[0]) {
addr->hash = UNIX_HASH_SIZE;
hash = d_backing_inode(path.dentry)->i_ino & (UNIX_HASH_SIZE - 1);
spin_lock(&unix_table_lock);
u->path = path;
list = &unix_socket_table[hash];
} else {
in unix_bind() (in which case u->addr->name->sun_path[0] will not be '\0') and
/* copy address information from listening to new sock*/
if (otheru->addr) {
refcount_inc(&otheru->addr->refcnt);
newu->addr = otheru->addr;
}
if (otheru->path.dentry) {
path_get(&otheru->path);
newu->path = otheru->path;
}
in unix_stream_connect(). And once ->addr is non-NULL, it's never changed,
and ->addr->name contents is never modified afterwards. So we would have
to had the same condition (non-NULL ->path.dentry with '\0' in
->addr->name->sun_path[0]) at earlier point on the listener socket.
Looks like that should be impossible; what am I missing here? Incidentally,
how can the quoted fragment in in unix_stream_connect() be reached with NULL
otheru->addr? After all, otheru is unix_sock of a listener; how could
we possibly have found it if it had NULL ->addr?
Confused...
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC] apparently bogus logics in unix_find_other() since 2002
2019-02-10 4:24 [RFC] apparently bogus logics in unix_find_other() since 2002 Al Viro
@ 2019-02-11 3:19 ` Al Viro
2019-02-11 11:21 ` Solar Designer
1 sibling, 0 replies; 3+ messages in thread
From: Al Viro @ 2019-02-11 3:19 UTC (permalink / raw)
To: netdev; +Cc: Solar Designer, David Miller
On Sun, Feb 10, 2019 at 04:24:15AM +0000, Al Viro wrote:
>
> Looks like that should be impossible; what am I missing here? Incidentally,
> how can the quoted fragment in in unix_stream_connect() be reached with NULL
> otheru->addr? After all, otheru is unix_sock of a listener; how could
> we possibly have found it if it had NULL ->addr?
>
> Confused...
BTW, speaking of interesting corner cases in AF_UNIX: am I right assuming that
identical abstract names with different protocols are considered entirely
independent? Where is that thing (== abstract namespace) documented, anyway?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC] apparently bogus logics in unix_find_other() since 2002
2019-02-10 4:24 [RFC] apparently bogus logics in unix_find_other() since 2002 Al Viro
2019-02-11 3:19 ` Al Viro
@ 2019-02-11 11:21 ` Solar Designer
1 sibling, 0 replies; 3+ messages in thread
From: Solar Designer @ 2019-02-11 11:21 UTC (permalink / raw)
To: Al Viro; +Cc: netdev, David Miller
On Sun, Feb 10, 2019 at 04:24:22AM +0000, Al Viro wrote:
> In "net/unix/af_unix.c: Set ATIME on socket inode" (back in
> 2002) we'd grown something rather odd in unix_find_other(). In the
> original patch it was
> u=unix_find_socket_byname(sunname, len, type, hash);
> - if (!u)
> + if (u) {
> + struct dentry *dentry;
> + dentry = u->protinfo.af_unix.dentry;
> + if (dentry)
> + UPDATE_ATIME(dentry->d_inode);
> + } else
> goto fail;
It's this commit:
https://github.com/dmgerman/linux-bitkeeper/commit/80cbc5b9c7393c4456236543ca1e639ea0841c19
There are two hunks in that patch: one after "if (sunname->sun_path[0])"
and the other after "else". I just did some more digging and found the
private discussion of the time, as well as a previous revision of the
patch (against 2.2.21, whereas the committed one was against 2.4.x of
the same era). Even the earliest revision I found already has both
hunks. I couldn't find any discussion as to why the second hunk was
possibly needed. It is quite possible that I had added it in error.
The original problem this patch addressed was stmpclean deleting sockets
that were still actively used - specifically, PostgreSQL's. I found
that I also tested the patch on /dev/log and X11 sockets. However, I
can't find any indication of me ever testing with the first hunk only,
so it's quite possible I wrote both hunks at once and only tested both.
> These days the code is
>
> u = unix_find_socket_byname(net, sunname, len, type, hash);
> if (u) {
> struct dentry *dentry;
> dentry = unix_sk(u)->path.dentry;
> if (dentry)
> touch_atime(&unix_sk(u)->path);
> } else
> goto fail;
>
> but the logics is the same. It's the abstract address case - we have
> '\0' in sunname->sun_path[0]. How in hell could that possibly have
> non-NULL ->path.dentry and what would it be?
This is probably in fact impossible.
I think it'd make sense to drop this logic, reverting to:
if (!u)
goto fail;
and then see if atime on an actively used socket in /tmp or on /dev/log
keeps getting updated (due to the first hunk of the above commit).
Alexander
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-02-11 3:19 ` Al Viro
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