af8d3c7c00
The PPPIOCDETACH ioctl effectively tries to "close" the given ppp file before f_count has reached 0, which is fundamentally a bad idea. It does check 'f_count < 2', which excludes concurrent operations on the file since they would only be possible with a shared fd table, in which case each fdget() would take a file reference. However, it fails to account for the fact that even with 'f_count == 1' the file can still be linked into epoll instances. As reported by syzbot, this can trivially be used to cause a use-after-free. Yet, the only known user of PPPIOCDETACH is pppd versions older than ppp-2.4.2, which was released almost 15 years ago (November 2003). Also, PPPIOCDETACH apparently stopped working reliably at around the same time, when the f_count check was added to the kernel, e.g. see https://lkml.org/lkml/2002/12/31/83. Also, the current 'f_count < 2' check makes PPPIOCDETACH only work in single-threaded applications; it always fails if called from a multithreaded application. All pppd versions released in the last 15 years just close() the file descriptor instead. Therefore, instead of hacking around this bug by exporting epoll internals to modules, and probably missing other related bugs, just remove the PPPIOCDETACH ioctl and see if anyone actually notices. Leave a stub in place that prints a one-time warning and returns EINVAL. Reported-by: syzbot+16363c99d4134717c05b@syzkaller.appspotmail.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Eric Biggers <ebiggers@google.com> Acked-by: Paul Mackerras <paulus@ozlabs.org> Reviewed-by: Guillaume Nault <g.nault@alphalink.fr> Tested-by: Guillaume Nault <g.nault@alphalink.fr> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
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.