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charset="UTF-8" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E52942000C X-Rspam-User: X-Stat-Signature: 5iedeitgbhwheupf585a9rs83emjjof5 X-Spamd-Result: default: False [2.27 / 9.00]; SORBS_IRL_BL(3.00)[209.85.166.44:from]; BAYES_HAM(-1.83)[86.19%]; SUBJECT_HAS_UNDERSCORES(1.00)[]; RCVD_NO_TLS_LAST(0.10)[]; MIME_GOOD(-0.10)[text/plain]; BAD_REP_POLICIES(0.10)[]; R_SPF_ALLOW(0.00)[+ip4:209.85.128.0/17]; R_DKIM_ALLOW(0.00)[google.com:s=20210112]; RCPT_COUNT_SEVEN(0.00)[9]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; DMARC_POLICY_ALLOW(0.00)[google.com,reject]; TO_MATCH_ENVRCPT_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; DKIM_TRACE(0.00)[google.com:+]; PREVIOUSLY_DELIVERED(0.00)[linux-mm@kvack.org]; ARC_NA(0.00)[]; ARC_SIGNED(0.00)[hostedemail.com:s=arc-20220608:i=1]; TO_DN_EQ_ADDR_SOME(0.00)[] X-HE-Tag: 1670279001-791019 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 Mon, Dec 5, 2022 at 11:13 PM 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/ > > . > > 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, Yeah, that was sort of my thinking. > but due to the insufficient locking > it most likely is, right? To be honest, I don't really know how bad this is - pretty much the only thing we're doing here is to change the VMA end. I don't know if that messes up the address_space's interval tree or something? I have no clue how that data structure looks.