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Tue, 21 Sep 2021 20:33:38 -0700 (PDT) Received: from sc2-haas01-esx0118.eng.vmware.com ([66.170.99.1]) by smtp.gmail.com with ESMTPSA id o15sm537269pfg.14.2021.09.21.20.33.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Sep 2021 20:33:37 -0700 (PDT) From: Nadav Amit X-Google-Original-From: Nadav Amit To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Nadav Amit , Peter Xu , Andrea Arcangeli , stable@vger.kernel.org Subject: [PATCH] userfaultfd: fix a race between writeprotect and exit_mmap() Date: Tue, 21 Sep 2021 13:02:47 -0700 Message-Id: <20210921200247.25749-1-namit@vmware.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: CADE090000AF Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b="a/IqhzdD"; dmarc=pass (policy=none) header.from=gmail.com; spf=none (imf23.hostedemail.com: domain of mail-pj1-f52.google.com has no SPF policy when checking 209.85.216.52) smtp.helo=mail-pj1-f52.google.com X-Stat-Signature: qsbnnu3ggf9i6x9buo6t4u8nbyth3dcf X-HE-Tag: 1632281619-405868 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.006583, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Nadav Amit A race is possible when a process exits, its VMAs are removed by exit_mmap() and at the same time userfaultfd_writeprotect() is called. The race was detected by KASAN on a development kernel, but it appears to be possible on vanilla kernels as well. Use mmget_not_zero() to prevent the race as done in other userfaultfd operations. Cc: Peter Xu Cc: Andrea Arcangeli Cc: stable@vger.kernel.org Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to userf= aultfd ioctl") Signed-off-by: Nadav Amit --- fs/userfaultfd.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 003f0d31743e..22bf14ab2d16 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1827,9 +1827,15 @@ static int userfaultfd_writeprotect(struct userfau= ltfd_ctx *ctx, if (mode_wp && mode_dontwake) return -EINVAL; =20 - ret =3D mwriteprotect_range(ctx->mm, uffdio_wp.range.start, - uffdio_wp.range.len, mode_wp, - &ctx->mmap_changing); + if (mmget_not_zero(ctx->mm)) { + ret =3D mwriteprotect_range(ctx->mm, uffdio_wp.range.start, + uffdio_wp.range.len, mode_wp, + &ctx->mmap_changing); + mmput(ctx->mm); + } else { + return -ESRCH; + } + if (ret) return ret; =20 --=20 2.25.1