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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id ca18e2360f4ac-834efcaeadasm73257639f.26.2024.10.04.05.29.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Oct 2024 05:29:54 -0700 (PDT) Date: Fri, 4 Oct 2024 08:29:51 -0400 From: Peter Xu To: Manas 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: 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: 087F018001B X-Stat-Signature: yjgueo8qp3cqfnqfw5shwsddwbduybe3 X-HE-Tag: 1728044998-372020 X-HE-Meta: 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 YnXGhsll 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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 Fri, Oct 04, 2024 at 03:43:12PM +0530, Manas wrote: > Hi Peter, thanks for reviewing. > > On 03.10.2024 12:41, Peter Xu wrote: > > 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; > > > This will lead to `-Wint-conversion` error in the assignment. We can either do a > cast like the following: > > struct address_space *mapping = (struct address_space *)(vma->vm_file && vma->vm_file->f_mapping); > > But I am not sure if it is the canonical way of doing it. It will also lead to > warning about pointer from integer casting. > > Or will a conditional like this work here? > > struct address_space *mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL; Sorry, that was a pretty stupid mistake of mine, just to show what I meant without any compilation tests. Yes this one. Thanks, > > 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 > > > > -- > Manas > -- Peter Xu