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t=1682967735; bh=9QPEkjebC4OaH1v6v+RGKCi2h6hrTwDOyzCb/vnJn5I=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=NoqLhz0cLUcBJW4qHoSw9EOCu0x7TippyuYpbP5hgaGdGyWOHdfMGQ57WBBdNVo7s 0rwLmi6x5NfkQAIjUswiJOWSaGewys68AsoaaJOfKYzs592g+V1bJ4ASSIMgPQPr9g fslSLh09yi21do7wFk8ayX3oh0OJyEF3JrszScec4ZkkwKndF1Fq16WBH1BcNU08lz Zqm1F4AdDrn//VvO7wtH1+n650oXwLSKCrHp0eqFT3BiWKWJHFOO1gNtw8ZSElUuP2 hEpW+JTn9r9utML7j55PXhLLOF9hKN2wwlJryOsm5EIxJrTYYdhk06AX0enXk/fuwV kI9sAj/s4eLOQ== Received: by mail-ed1-f54.google.com with SMTP id 4fb4d7f45d1cf-50bc4b88998so2834558a12.3 for ; Mon, 01 May 2023 12:02:15 -0700 (PDT) X-Gm-Message-State: AC+VfDwi/O3c5hOG+Q/rsy561tSmJJAHfCVwIOtOyMiORMrw7iWYOT1w fHX1MSDpGQr5nmqu4xJIgptnemIs/gLIsW+yScbzYw== X-Google-Smtp-Source: ACHHUZ6zV6tmNwgGbZSj/tAPjzw/u56lqCpK3jfeQIEg5ZZJCP33LO2ERSqQLQEQ5Q10BpG1mtr6OX/twGNMC1UT2O0= X-Received: by 2002:aa7:c3d9:0:b0:4fe:19cb:4788 with SMTP id l25-20020aa7c3d9000000b004fe19cb4788mr5988608edr.42.1682967732371; Mon, 01 May 2023 12:02:12 -0700 (PDT) MIME-Version: 1.0 References: <6f3aea05c9cc46094b029cbd1138d163c1ae7f9d.1682890156.git.lstoakes@gmail.com> In-Reply-To: <6f3aea05c9cc46094b029cbd1138d163c1ae7f9d.1682890156.git.lstoakes@gmail.com> From: Andy Lutomirski Date: Mon, 1 May 2023 12:02:00 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 3/3] mm: perform the mapping_map_writable() check after call_mmap() To: Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Matthew Wilcox , Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , linux-fsdevel@vger.kernel.org, Jan Kara , Hugh Dickins Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 88CE240012 X-Stat-Signature: rd9443469z3jkdao13xt1piobp6wo5fd X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1682967737-182392 X-HE-Meta: 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 JQn4Ql7J A00+lqfUJdeA/ouuX8j1fwV95axoDaFfdNibhor8bM9r5Py7kd2d6KUA83OZWUeLoEs9sYH7tli7Mjt1oODM8vgwuUAYsh+jiEv1g8tKmMflH/AvOi2Z1GBcX7vFOy3rkNpo9b4rq+FBN3IfYoDDoE9KWAYnm04hkveLBCiiuMIPRm6riVz84UUmM6C1Qx7Sj/OkSI7jIhhQ60TwqoimqU1ZYHr/KppuRexkWezhQhUelWWgRKbT+60ZahqIIC3ldZbgHP57MnoW3Xrfewmhp+unIywba9FJDhfzBm5L3Ft7f6JcDBwqPY4bxoXt+5RZKyp5I3YA/3uJMajv71uDjligNA+nYJLSUyaklm+IS6uMpKbTXjNrO2QxwRPzwTDfL1ct4m9BdHzY2/VFkm3Ltavoxz+2SueIQFkkQgOdWuQVEw8dQIZkKtpWgNTuCEaYRHOn5 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Apr 30, 2023 at 3:26=E2=80=AFPM Lorenzo Stoakes wrote: > > In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity t= o > clear VM_MAYWRITE, we must be able to invoke the appropriate vm_ops->mmap= () > handler to do so. We would otherwise fail the mapping_map_writable() chec= k > before we had the opportunity to avoid it. Is there any reason this can't go before patch 3? If I'm understanding correctly, a comment like the following might make this a lot more comprehensible: > > This patch moves this check after the call_mmap() invocation. Only memfd > actively denies write access causing a potential failure here (in > memfd_add_seals()), so there should be no impact on non-memfd cases. > > This patch makes the userland-visible change that MAP_SHARED, PROT_READ > mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D217238 > Signed-off-by: Lorenzo Stoakes > --- > mm/mmap.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 646e34e95a37..1608d7f5a293 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2642,17 +2642,17 @@ unsigned long mmap_region(struct file *file, unsi= gned long addr, > vma->vm_pgoff =3D pgoff; > > if (file) { > - if (is_shared_maywrite(vm_flags)) { > - error =3D mapping_map_writable(file->f_mapping); > - if (error) > - goto free_vma; > - } > - > vma->vm_file =3D get_file(file); > error =3D call_mmap(file, vma); > if (error) > goto unmap_and_free_vma; > /* vm_ops->mmap() may have changed vma->flags. Check for writability now. = */ > + if (vma_is_shared_maywrite(vma)) { > + error =3D mapping_map_writable(file->f_mapping); > + if (error) > + goto close_and_free_vma; > + } > + Alternatively, if anyone is nervous about the change in ordering here, there could be a whole new vm_op like adjust_vma_flags() that happens before any of this. --Andy