From: Davidlohr Bueso <dave@stgolabs.net> To: akpm@linux-foundation.org, aarcange@redhat.com Cc: joe.lawrence@redhat.com, gareth.evans@contextis.co.uk, linux-kernel@vger.kernel.org, linux-mm@kvack.org, dave@stgolabs.net, stable@kernel.org, Davidlohr Bueso <dbueso@suse.de> Subject: [PATCH 1/2] Revert "ipc/shm: Fix shmat mmap nil-page protection" Date: Thu, 3 May 2018 13:32:42 -0700 Message-ID: <20180503203243.15045-2-dave@stgolabs.net> (raw) In-Reply-To: <20180503203243.15045-1-dave@stgolabs.net> 95e91b831f87 (ipc/shm: Fix shmat mmap nil-page protection) worked on the idea that we should not be mapping as root addr=0 and MAP_FIXED. However, it was reported that this scenario is in fact valid, thus making the patch both bogus and breaks userspace as well. For example X11's libint10.so relies on shmat(1, SHM_RND) for lowmem initialization[1]. [1] https://cgit.freedesktop.org/xorg/xserver/tree/hw/xfree86/os-support/linux/int10/linux.c#n347 Reported-by: Joe Lawrence <joe.lawrence@redhat.com> Reported-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Davidlohr Bueso <dbueso@suse.de> --- ipc/shm.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/ipc/shm.c b/ipc/shm.c index 0075990338f4..b81d53c8f459 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -1371,13 +1371,8 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, if (addr) { if (addr & (shmlba - 1)) { - /* - * Round down to the nearest multiple of shmlba. - * For sane do_mmap_pgoff() parameters, avoid - * round downs that trigger nil-page and MAP_FIXED. - */ - if ((shmflg & SHM_RND) && addr >= shmlba) - addr &= ~(shmlba - 1); + if (shmflg & SHM_RND) + addr &= ~(shmlba - 1); /* round down */ else #ifndef __ARCH_FORCE_SHMLBA if (addr & ~PAGE_MASK) -- 2.13.6
next prev parent reply index Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-05-03 20:32 [PATCH -next 0/2] ipc/shm: shmat() fixes around nil-page Davidlohr Bueso 2018-05-03 20:32 ` Davidlohr Bueso [this message] 2018-05-03 20:49 ` [PATCH 2/2] ipc/shm: fix shmat() nil address after round-down when remapping Davidlohr Bueso 2018-05-10 18:17 ` [PATCH -next 0/2] ipc/shm: shmat() fixes around nil-page Vlastimil Babka 2018-05-14 16:19 ` Davidlohr Bueso
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