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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1swk3q-0000000Agm7-1p4w; Fri, 04 Oct 2024 15:17:42 +0000 Date: Fri, 4 Oct 2024 16:17:42 +0100 From: Matthew Wilcox To: manas18244@iiitd.ac.in Cc: Andrew Morton , Peter Xu , 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 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241004-fix-null-deref-v3-1-f9459b1cc95f@iiitd.ac.in> X-Rspamd-Queue-Id: 226D32000A X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: he13s3wboscio1uxc1gc1ue4khgxmyyi X-HE-Tag: 1728055065-415762 X-HE-Meta: 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 M+BQd9BQ E/CI7QqeMZzRPM4MPJJacBkqocBFBDCQd4B8qiDpk3MK76oM+Re9rbEcQ7RChQQXGQhHyBex2qbPi66lHU7l9We9PdXVYtsHSygpC4I5WxwFcozsSmJKYwHNKuBeWArEhTSlHyKcA0cOA+d/6/ZUOdN34AJntmahM4RAa64XKC8zHWRaLfNTCgSIYDw8jK0ACztujQLmFLY9Z8WLvSEvWzreccMUOJ+eyr9WArFfgaVi7g5PE9Fmp8C+u4IEBTrxVUg4C+wpdMebFnnoPXaCzpWs/1tj442vAs4ltWK8JmELPizHMsqRWBrwSUm4/SWgQZ3kJZePFPgfdCFv02eW8TAlMhd96koFc7xVEjHs0GiOnzkMT2fdxEeIwUA== 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 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.