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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7ae6b39a6f8sm63735385a.41.2024.10.03.09.41.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Oct 2024 09:41:36 -0700 (PDT) Date: Thu, 3 Oct 2024 12:41:34 -0400 From: Peter Xu To: manas18244@iiitd.ac.in Cc: Andrew Morton , Shuah Khan , Anup Sharma , linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+093d096417e7038a689b@syzkaller.appspotmail.com Subject: Re: [PATCH] Fixes: null pointer dereference in pfnmap_lockdep_assert Message-ID: References: <20241003-fix-null-deref-v1-1-0a45df9d016a@iiitd.ac.in> MIME-Version: 1.0 In-Reply-To: <20241003-fix-null-deref-v1-1-0a45df9d016a@iiitd.ac.in> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 3BF1720008 X-Stat-Signature: ic3di54goateaie8qmrqrb9dyztjtw8a X-HE-Tag: 1727973701-520346 X-HE-Meta: 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 3Pa69Y5C 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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 Thu, Oct 03, 2024 at 09:31:06PM +0530, Manas via B4 Relay wrote: > From: Manas > > syzbot has pointed to a possible null pointer dereference in > pfnmap_lockdep_assert. vm_file member of vm_area_struct is being > dereferenced without any checks. > > This fix returns if vm_file member in vm_area_struct is NULL. > > Reported-by: syzbot+093d096417e7038a689b@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=093d096417e7038a689b > --- > This bug[1] triggers a general protection fault in follow_pfnmap_start > function. An assertion pfnmap_lockdep_assert inside this function > dereferences vm_file member of vm_area_struct. And panic gets triggered > when vm_file is NULL. > > This patch returns from the assertion pfnmap_lockdep_assert if vm_file > is found to be NULL. > > [1] https://syzkaller.appspot.com/bug?extid=093d096417e7038a689b > > Signed-off-by: Manas Thanks for the patch! > --- > mm/memory.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index 2366578015ad..b152a95e543f 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -6346,6 +6346,9 @@ 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 > + if (!vma->vm_file) > + return; > + Hmm I guess I wasn't careful enough here as I was mostly only thinking about file mappings, but I just notice we have other pfnmaps like the vvar mappings.. the mapping var can also already be reused later when available. Logically even if !vm_file we can still check against mmap write lock. So would it be better to do this instead: struct address_space *mapping = vma->vm_file && vma->vm_file->f_mapping; if (mapping) 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)); ? > struct address_space *mapping = vma->vm_file->f_mapping; > > if (mapping) > > --- > base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc > change-id: 20241003-fix-null-deref-6bfa0337efc3 > > Best regards, > -- > Manas > > > -- Peter Xu