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Tue, 27 Feb 2024 09:22:37 -0800 (PST) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id x92-20020a17090a6c6500b00298d8804ba8sm9585587pjj.46.2024.02.27.09.22.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Feb 2024 09:22:36 -0800 (PST) Date: Tue, 27 Feb 2024 09:22:35 -0800 From: Kees Cook To: "Eric W. Biederman" Cc: Jan Bujak , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: Recent-ish changes in binfmt_elf made my program segfault Message-ID: <202402270911.961702D7D6@keescook> References: <202402261821.F2812C9475@keescook> <878r35rkc4.fsf@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <878r35rkc4.fsf@email.froward.int.ebiederm.org> X-Rspamd-Queue-Id: 67EA72001C X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: zm131ndxgx1okm51duwizwu7cuebo3hw X-HE-Tag: 1709054558-361479 X-HE-Meta: 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 wGNQwvEd 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.010484, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Feb 27, 2024 at 09:35:39AM -0600, Eric W. Biederman wrote: > Kees Cook writes: > > > On Tue, Jan 23, 2024 at 12:23:27AM +0900, Jan Bujak wrote: > >> On 1/22/24 23:54, Pedro Falcato wrote: > >> > Hi! > >> > > >> > Where did you get that linker script? > >> > > >> > FWIW, I catched this possible issue in review, and this was already > >> > discussed (see my email and Eric's reply): > >> > https://lore.kernel.org/all/CAKbZUD3E2if8Sncy+M2YKncc_Zh08-86W6U5wR0ZMazShxbHHA@mail.gmail.com/ > >> > > >> > This was my original testcase > >> > (https://github.com/heatd/elf-bug-questionmark), which convinced the > >> > loader to map .data over a cleared .bss. Your bug seems similar, but > >> > does the inverse: maps .bss over .data. > >> > > >> > >> I wrote the linker script myself from scratch. > > > > Do you still need this addressed, or have you been able to adjust the > > linker script? (I ask to try to assess the priority of needing to fix > > this behavior change...) > > Kees, I haven't had a chance to test this yet but it occurred to me > that there is an easy way to handle this. In our in-memory copy > of the elf program headers we can just merge the two segments > together. > > I believe the diff below accomplishes that, and should fix issue. > > Signed-off-by: "Eric W. Biederman" > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index 5397b552fbeb..01df7dd1f3b4 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -924,6 +926,31 @@ static int load_elf_binary(struct linux_binprm *bprm) > elf_ppnt = elf_phdata; > for (i = 0; i < elf_ex->e_phnum; i++, elf_ppnt++) > switch (elf_ppnt->p_type) { > + case PT_LOAD: > + { > + /* > + * Historically linux ignored all but the > + * final .bss segment. Now that linux honors > + * all .bss segments, a .bss segment that > + * logically is not overlapping but is > + * overlapping when it's edges are rounded up > + * to page size causes programs to fail. > + * > + * Handle that case by merging .bss segments > + * into the segment they follow. > + */ > + if (((i + 1) >= elf_ex->e_phnum) || > + (elf_ppnt[1].p_type != PT_LOAD) || > + (elf_ppnt[1].p_filesz != 0)) > + continue; > + unsigned long end = > + elf_ppnt[0].p_vaddr + elf_ppnt[0].p_memsz; > + if (elf_ppnt[1].p_vaddr != end) > + continue; > + elf_ppnt[0].p_memsz += elf_ppnt[1].p_memsz; > + elf_ppnt[1].p_type = PT_NULL; > + break; > + } > case PT_GNU_STACK: > if (elf_ppnt->p_flags & PF_X) > executable_stack = EXSTACK_ENABLE_X; I don't think this is safe -- it isn't looking at flags, etc. e.g., something like this could break:   Type  Offset   VirtAddr  PhysAddr  FileSiz  MemSiz   Flg Align   LOAD  0x003000 0x12000   0x12000   0x001000 0x001000 R E 0x1000   LOAD  0x004000 0x13000   0x13000   0x000000 0x001000 RW  0x1000 Hmm -- Kees Cook