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Wed, 18 Oct 2023 22:41:03 -0700 (PDT) Received: from localhost ([102.36.222.112]) by smtp.gmail.com with ESMTPSA id i6-20020adfe486000000b0032415213a6fsm3580699wrm.87.2023.10.18.22.41.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Oct 2023 22:41:02 -0700 (PDT) Date: Thu, 19 Oct 2023 08:40:59 +0300 From: Dan Carpenter To: Baoquan He Cc: Andrew Morton , Philip Li , oe-kbuild@lists.linux.dev, Lorenzo Stoakes , lkp@intel.com, oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org, Linux Memory Management List Subject: Re: mm/vmalloc.c:3689 vread_iter() error: we previously assumed 'vm' could be null (see line 3667) Message-ID: <0eddb8b4-47a1-4d94-ae44-707addae77c8@kadam.mountain> References: <89caf59a-d3b9-409d-b1ae-9e370cb9ee7d@kadam.mountain> <20231018085248.6f3f36101cbdfe0990c8b467@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 224B340010 X-Stat-Signature: 43iwq9cexaqrs51x4cy8ndisi7oqmob8 X-HE-Tag: 1697694064-295604 X-HE-Meta: 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 Umeg/Kp4 EvIe6llR3WkX9tj0gTaeFXkf1OegVnB+5g5CRq0hl546e9WZ6Y4ZfUFOCeiTfA5jkdluoWiLYgBXMbSAOL0KhGiIT7cI8irilYs8gIp8FCiXXUty8aoGSywqMTphFUCKAL8PVfVFDLB7/hGth6jSORkurja0C6EDcCpMAD7uWP3wkSUqU9tvwyxvIbWU1mKzhosWL+LwNEEDCUXRfbWZ2DeOxe8XVHz8gDhNOccprc0ocEd0G1M9yy/Uitipfs1xUxGvLnch847SZa5PvNdL6B/DFi3HW69IbAcG293T08Wxif3wRVdTytQ07nAycLdcvPoZjLFURCQGVaKhS2jKUQ5O3fGPsFgLdh61Xb9DEm8+Yj6hLtQKoRnJ1UQ== 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 Thu, Oct 19, 2023 at 10:28:21AM +0800, Baoquan He wrote: > On 10/18/23 at 08:52am, Andrew Morton wrote: > > On Wed, 18 Oct 2023 23:15:31 +0800 Baoquan He wrote: > > > > > From: Baoquan He > > > Date: Wed, 18 Oct 2023 22:50:14 +0800 > > > Subject: [PATCH] mm/vmalloc: fix the unchecked dereference warning in vread_iter() > > > Content-type: text/plain > > > > > > LKP reported smatch warning as below: > > > > > > =================== > > > smatch warnings: > > > mm/vmalloc.c:3689 vread_iter() error: we previously assumed 'vm' could be null (see line 3667) > > > ...... > > > 06c8994626d1b7 @3667 size = vm ? get_vm_area_size(vm) : va_size(va); > > > ...... > > > 06c8994626d1b7 @3689 else if (!(vm->flags & VM_IOREMAP)) > > > ^^^^^^^^^ > > > Unchecked dereference > > > ===================== > > > > > > So add checking on whether 'vm' is not null when dereferencing it in > > > vread_iter(). This mutes smatch complaint. > > > > > > ... > > > > > > --- a/mm/vmalloc.c > > > +++ b/mm/vmalloc.c > > > @@ -3813,7 +3813,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count) > > > > > > if (flags & VMAP_RAM) > > > copied = vmap_ram_vread_iter(iter, addr, n, flags); > > > - else if (!(vm->flags & VM_IOREMAP)) > > > + else if (!(vm && (vm->flags & VM_IOREMAP))) > > > copied = aligned_vread_iter(iter, addr, n); > > > else /* IOREMAP area is treated as memory hole */ > > > copied = zero_iter(iter, n); > > > > So is this not a real runtime bug? We're only doing this to suppress a > > smatch warning? > > > > If so, can we please include a description of *why* this wasn't a bug? > > What conditions ensure that vm!=NULL at this point? > > I think this is not a real runtime bug. The only chance it can hapen is > when (flags == VMAP_BLOCK) is true. That has been warned and could never > happen. I updated patch log and paste v2 here. > > /* > * VMAP_BLOCK indicates a sub-type of vm_map_ram area, need > * be set together with VMAP_RAM. > */ > WARN_ON(flags == VMAP_BLOCK); > > if (!vm && !flags) > continue; > > Thanks. If you want you could just ignore the warning. It's a one time warning so we won't send the mail again and if people have questions about it, they can just look it up on lore. The truth is when I was reviewing this code the first time I got mixed up between flags and vm->flags so that's part of why I reported it. Smatch ignores the WARN_ON(). Historically WARN_ON() has been useless for indicating whether something can happen or not. These days, WARN_ON() is treated as a syzkaller bug so we prefer pr_warn() if something can actually happen. We still see a lot of WARN_ON()s happening in real life so I'm not eager to make Smatch treat them like a BUG_ON(). Also, sadly, even if we changed the WARN_ON() to a BUG_ON() it still wouldn't silence the warning because Smatch is not quite clever enough to parse that. regards, dan carpenter