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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id e9e14a558f8ab-3a37a7fbe19sm19960085ab.34.2024.10.08.12.27.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2024 12:27:57 -0700 (PDT) Date: Tue, 8 Oct 2024 15:27:54 -0400 From: Peter Xu To: Matthew Wilcox Cc: manas18244@iiitd.ac.in, Andrew Morton , Shuah Khan , Anup Sharma , linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+093d096417e7038a689b@syzkaller.appspotmail.com Subject: Re: [PATCH v3] Fixes: null pointer dereference in pfnmap_lockdep_assert Message-ID: References: <20241004-fix-null-deref-v3-1-f9459b1cc95f@iiitd.ac.in> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 9CDC84000C X-Stat-Signature: gx3fynteu3diotsz5aaf6k6eqjaf36sg X-Rspam-User: X-HE-Tag: 1728415683-431711 X-HE-Meta: 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 /SWn7h3u 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 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: List-Subscribe: List-Unsubscribe: On Mon, Oct 07, 2024 at 09:23:47AM -0400, Peter Xu wrote: > On Fri, Oct 04, 2024 at 04:17:42PM +0100, Matthew Wilcox wrote: > > On Fri, Oct 04, 2024 at 07:15:48PM +0530, Manas via B4 Relay wrote: > > > +++ b/mm/memory.c > > > @@ -6346,10 +6346,10 @@ static inline void pfnmap_args_setup(struct follow_pfnmap_args *args, > > > static inline void pfnmap_lockdep_assert(struct vm_area_struct *vma) > > > { > > > #ifdef CONFIG_LOCKDEP > > > - struct address_space *mapping = vma->vm_file->f_mapping; > > > + struct address_space *mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL; > > > > Overly long and complex line. Much simpler to write: > > > > struct address_space *mapping = NULL; > > > > if (vma->vm_file) > > mapping = vma->vm_file->f_mapping; > > > > > if (mapping) > > > - lockdep_assert(lockdep_is_held(&vma->vm_file->f_mapping->i_mmap_rwsem) || > > > + lockdep_assert(lockdep_is_held(&mapping->i_mmap_rwsem) || > > > lockdep_is_held(&vma->vm_mm->mmap_lock)); > > > else > > > lockdep_assert(lockdep_is_held(&vma->vm_mm->mmap_lock)); > > > > This one should have been lockdep_assert_held(&vma->vm_mm->mmap_lock). > > > > I'm not sure that the previous one is correct. The > > lockdep_assert_held() macro is pretty careful about checking > > LOCK_STATE_NOT_HELD to avoid the LOCK_STATE_UNKNOWN possibility. > > But I'll leave that for Peter to fix. > > Indeed.. > > Then looks like we could have quite a few other places in Linux that can > have used this wrong.. when the assert wants to check against either of the > two locks (one mutex or rcu read lock, for example) is held. > > I'll send a patch after this one lands. Just to follow this up and leave a record: I had a closer look today and then quickly I found above should be all fine (similar to all kernel usages like this, for example, rcu_dereference_check()). The trick is LOCK_STATE_NOT_HELD is defined as 0: #define LOCK_STATE_UNKNOWN -1 #define LOCK_STATE_NOT_HELD 0 #define LOCK_STATE_HELD 1 So this: #define lockdep_assert_held(l) \ lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD) Is the same to: #define lockdep_assert_held(l) \ lockdep_assert(lockdep_is_held(l)) The lockdep_assert() was introduced exactly for such >1 lock assertion use cases, in this commit: commit d19c81378829e5d774c951219c5a973965b9202c Author: Peter Zijlstra Date: Mon Aug 2 18:59:56 2021 +0800 locking/lockdep: Provide lockdep_assert{,_once}() helpers Extract lockdep_assert{,_once}() helpers to more easily write composite assertions like, for example: lockdep_assert(lockdep_is_held(&drm_device.master_mutex) || lockdep_is_held(&drm_file.master_lookup_lock)); Thanks, -- Peter Xu