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Mon, 5 Dec 2022 22:26:16 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id Egi7LghwjmO9dQAAGKfGzw (envelope-from ); Mon, 05 Dec 2022 22:26:16 +0000 Message-ID: <6eb002c8-0e31-7c9f-bb3d-81c4430b296c@suse.cz> Date: Mon, 5 Dec 2022 23:26:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH v2] mmap: Fix do_brk_flags() modifying obviously incorrect VMAs Content-Language: en-US From: Vlastimil Babka To: Jann Horn , Andrew Morton Cc: Liam Howlett , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Yu Zhao , Jason Donenfeld , Matthew Wilcox , SeongJae Park References: <20221205192304.1957418-1-Liam.Howlett@oracle.com> <20221205123250.3fc552d96fcca5dc58be8443@linux-foundation.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 80FF6140007 X-Stat-Signature: z9izey5u81wfj3c9cptqqs74goyx98zs X-Spamd-Result: default: False [0.22 / 9.00]; SUBJECT_HAS_UNDERSCORES(1.00)[]; BAYES_HAM(-0.38)[70.84%]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; R_SPF_ALLOW(-0.20)[+ip4:195.135.220.0/24]; MIME_GOOD(-0.10)[text/plain]; RCVD_NO_TLS_LAST(0.10)[]; FROM_EQ_ENVFROM(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCPT_COUNT_SEVEN(0.00)[9]; MIME_TRACE(0.00)[0:+]; RCVD_COUNT_THREE(0.00)[4]; ARC_NA(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_SIGNED(0.00)[hostedemail.com:s=arc-20220608:i=1]; FROM_HAS_DN(0.00)[]; DMARC_NA(0.00)[suse.cz]; TO_DN_SOME(0.00)[]; TO_DN_EQ_ADDR_SOME(0.00)[] X-Rspam-User: X-HE-Tag: 1670279178-126087 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 12/5/22 23:13, Vlastimil Babka wrote: > On 12/5/22 22:55, Jann Horn wrote: >> On Mon, Dec 5, 2022 at 9:32 PM Andrew Morton wrote: >>> On Mon, 5 Dec 2022 19:23:17 +0000 Liam Howlett wrote: >>> > Add more sanity checks to the VMA that do_brk_flags() will expand. >>> > Ensure the VMA matches basic merge requirements within the function >>> > before calling can_vma_merge_after(). >>> >>> I't unclear what's actually being fixed here. >>> >>> Why do you feel we need the above changes? >>> >>> > Drop the duplicate checks from vm_brk_flags() since they will be >>> > enforced later. >>> > >>> > Fixes: 2e7ce7d354f2 ("mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()") >>> >>> Fixes in what way? Removing the duplicate checks? >> >> The old code would expand file VMAs on brk(), which is functionally >> wrong and also dangerous in terms of locking because the brk() path >> isn't designed for file VMAs and therefore doesn't lock the file >> mapping. Checking can_vma_merge_after() ensures that new anonymous >> VMAs can't be merged into file VMAs. >> >> See https://lore.kernel.org/linux-mm/CAG48ez1tJZTOjS_FjRZhvtDA-STFmdw8PEizPDwMGFd_ui0Nrw@mail.gmail.com/ And yeah, that URL should have been a Link: in the patch. And the scenario it's fixing described in a bit more detail? > I guess the point is that if we fix it still within 6.1, we don't have to > devise how exactly this is exploitable, but due to the insufficient locking > it most likely is, right?