New: Autobind in unix domain sockets always requires call to bind

https://bugzilla.kernel.org/show_bug.cgi?id=104561

Bug ID: 104561
Summary: Autobind in unix domain sockets always requires call
to bind
Product: Documentation
Version: unspecified
Hardware: All
OS: Linux
Status: NEW
Severity: normal
Priority: P1
Component: man-pages
Assignee: documentation_man-pages-ztI5WcYan/[email protected]
Reporter: [email protected]
Regression: No

Created attachment 187571
--> https://bugzilla.kernel.org/attachment.cgi?id=187571&action=edit
Example code that shows bind() is necessary for autobind

In "man 7 unix" it says:
"If a bind(2) call specifies addrlen as sizeof(sa_family_t), or the SO_PASSCRED socket option was specified for a socket that was not explicitly bound to an address, then the socket is autobound to an abstract address."

However, only setting SO_PASSCRED is not enough to autobind. You always have to call bind, as you can see in the attached example. If you run it, every call should succeed and getsockname reports that the autobind address has a size of 8 bytes.
Now remove lines 20-22, so the socket gets no longer explicitly bound. getsockname reports that the address size is 2 bytes (because bound_addr.sun_path is not used) and the call to "listen" fails.

So it seems the call to "bind" is necessary even if SO_PASSCRED is used.

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