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[ Upstream commit6d8c50dcb0] fchownat() doesn't even hold refcnt of fd until it figures out fd is really needed (otherwise is ignored) and releases it after it resolves the path. This means sock_close() could race with sockfs_setattr(), which leads to a NULL pointer dereference since typically we set sock->sk to NULL in ->release(). As pointed out by Al, this is unique to sockfs. So we can fix this in socket layer by acquiring inode_lock in sock_close() and checking against NULL in sockfs_setattr(). sock_release() is called in many places, only the sock_close() path matters here. And fortunately, this should not affect normal sock_close() as it is only called when the last fd refcnt is gone. It only affects sock_close() with a parallel sockfs_setattr() in progress, which is not common. Fixes:86741ec254("net: core: Add a UID field to struct sock.") Reported-by: shankarapailoor <shankarapailoor@gmail.com> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> Cc: Lorenzo Colitti <lorenzo@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.