From: Guillaume Nault <firstname.lastname@example.org> To: Eric Biggers <email@example.com> Cc: firstname.lastname@example.org, Paul Mackerras <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, Eric Biggers <firstname.lastname@example.org> Subject: Re: [PATCH v2] ppp: remove the PPPIOCDETACH ioctl Date: Thu, 24 May 2018 14:04:49 +0000 [thread overview] Message-ID: <20180524140449.GA1389@alphalink.fr> (raw) In-Reply-To: <email@example.com> On Wed, May 23, 2018 at 02:37:38PM -0700, Eric Biggers wrote: > From: Eric Biggers <firstname.lastname@example.org> > > 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: email@example.com > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: firstname.lastname@example.org > Signed-off-by: Eric Biggers <email@example.com> > --- > > v2: leave a stub in place, rather than removing the ioctl completely. > Thanks a lot for your help on this matter. BTW, netdev has its own rules wrt. stable backports. You didn't need to CC: stable@. David handles -stable submissions himself. Using a 'PATCH net' subject prefix would have made it clear that this patch was fixing some released code and should be considered for -stable backport. Reviewed-by: Guillaume Nault <firstname.lastname@example.org> Tested-by: Guillaume Nault <email@example.com>
next prev parent reply other threads:[~2018-05-24 14:04 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <firstname.lastname@example.org> 2018-05-14 6:11 ` KASAN: use-after-free Read in remove_wait_queue (2) Eric Biggers 2018-05-18 16:02 ` Guillaume Nault 2018-05-23 3:29 ` Eric Biggers 2018-05-23 3:59 ` [PATCH] ppp: remove the PPPIOCDETACH ioctl Eric Biggers 2018-05-23 13:57 ` Guillaume Nault 2018-05-23 15:56 ` David Miller 2018-05-23 21:17 ` Eric Biggers 2018-05-23 21:37 ` [PATCH v2] " Eric Biggers 2018-05-23 23:04 ` Paul Mackerras 2018-05-24 14:04 ` Guillaume Nault [this message] 2018-05-25 2:55 ` David Miller 2018-06-06 9:01 ` Walter Harms 2018-05-23 13:26 ` KASAN: use-after-free Read in remove_wait_queue (2) Guillaume Nault
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