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To: Miklos Szeredi Cc: syzbot , Andrew Morton , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Miklos Szeredi , syzkaller-bugs , Al Viro References: <000000000000b4684e05a2968ca6@google.com> From: Mike Kravetz Message-ID: Date: Tue, 12 May 2020 11:11:18 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9619 signatures=668687 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 suspectscore=0 mlxscore=0 adultscore=0 mlxlogscore=999 malwarescore=0 bulkscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2005120136 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9619 signatures=668687 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 mlxlogscore=999 malwarescore=0 adultscore=0 mlxscore=0 priorityscore=1501 lowpriorityscore=0 impostorscore=0 clxscore=1011 bulkscore=0 phishscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2005120136 Content-Transfer-Encoding: quoted-printable 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 5/12/20 8:04 AM, Miklos Szeredi wrote: > On Tue, Apr 7, 2020 at 12:06 AM Mike Kravetz = wrote: >> On 4/5/20 8:06 PM, syzbot wrote: >> >> The routine is_file_hugepages() is just comparing the file ops to hueg= tlbfs: >> >> if (file->f_op =3D=3D &hugetlbfs_file_operations) >> return true; >> >> Since the file is in an overlayfs, file->f_op =3D=3D ovl_file_operatio= ns. >> Therefore, length will not be rounded up to huge page size and we crea= te a >> mapping with incorrect size which leads to the BUG. >> >> Because of the code in mmap, the hugetlbfs mmap() routine assumes leng= th is >> rounded to a huge page size. I can easily add a check to hugetlbfs mm= ap >> to validate length and return -EINVAL. However, I think we really wan= t to >> do the 'round up' earlier in mmap. This is because the man page says: >> >> Huge page (Huge TLB) mappings >> For mappings that employ huge pages, the requirements for the a= rguments >> of mmap() and munmap() differ somewhat from the requirements = for map=E2=80=90 >> pings that use the native system page size. >> >> For mmap(), offset must be a multiple of the underlying huge pa= ge size. >> The system automatically aligns length to be a multiple of the = underly=E2=80=90 >> ing huge page size. >> >> Since the location for the mapping is chosen BEFORE getting to the hug= etlbfs >> mmap routine, we can not wait until then to round up the length. Is t= here a >> defined way to go from a struct file * to the underlying filesystem so= we >> can continue to do the 'round up' in early mmap code? >=20 > That's easy enough: >=20 > static inline struct file *real_file(struct file *file) > { > return file->f_op !=3D ovl_file_operations ? file : file->private_d= ata; > } >=20 > But adding more filesystem specific code to generic code does not > sound like the cleanest way to solve this... We can incorporate the above 'real_file' functionality in the filesystem specific routine is_file_hugepages(), and I think that would address this specific issue. I'll code that up. >> One other thing I noticed with overlayfs is that it does not contain a >> specific get_unmapped_area file_operations routine. I would expect it= to at >> least check for and use the get_unmapped_area of the underlying filesy= stem? >> Can someone comment if this is by design? >=20 > Not sure. What exactly is f_op->get_unmapped_area supposed to do? >=20 IIUC, filesystems can define their own routines to get addresses for mmap operations. Quite a few filesystems define get_unmapped_area. The generic mmap code does the following, get_area =3D current->mm->get_unmapped_area; if (file) { if (file->f_op->get_unmapped_area) get_area =3D file->f_op->get_unmapped_area; } else if (flags & MAP_SHARED) { /* * mmap_region() will call shmem_zero_setup() to create a file, * so use shmem's get_unmapped_area in case it can be huge. * do_mmap_pgoff() will clear pgoff, so match alignment. */ pgoff =3D 0; get_area =3D shmem_get_unmapped_area; } addr =3D get_area(file, addr, len, pgoff, flags); If the filesystem provides a get_unmapped_area, it will use it. I beleiv= e overlayfs prevents this from happening for the underlying filesystem. Perhaps we do need to add something like a call 'real_file' to this gener= ic code? I can't think of any other way to get to the underlying filesystem get_unmapped_area here. --=20 Mike Kravetz