Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S939089AbcKXLDa (ORCPT ); Thu, 24 Nov 2016 06:03:30 -0500 Received: from mail-wm0-f53.google.com ([74.125.82.53]:38119 "EHLO mail-wm0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936026AbcKXLD2 (ORCPT ); Thu, 24 Nov 2016 06:03:28 -0500 From: Miklos Szeredi To: linux-unionfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 6/7] ovl: intercept mmap Date: Thu, 24 Nov 2016 11:55:43 +0100 Message-Id: <1479984944-1017-8-git-send-email-mszeredi@redhat.com> X-Mailer: git-send-email 2.5.5 In-Reply-To: <1479984944-1017-1-git-send-email-mszeredi@redhat.com> References: <1479984944-1017-1-git-send-email-mszeredi@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3235 Lines: 126 ... in order to handle the corner case when the file is copied up after being opened read-only and mapped shared. Can be verified with the following script: - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - - cd / rm -rf /tmp/ovl-rorw-test mkdir /tmp/ovl-rorw-test cd /tmp/ovl-rorw-test cat << EOF > rorw-map.c #include #include #include #include #include int main(int argc, char *argv[]) { int rofd, rwfd; int ret; char buf[4]; char *addr; rofd = open(argv[1], O_RDONLY); if (rofd == -1) err(1, "ro open"); addr = mmap(NULL, 4, PROT_READ, MAP_SHARED, rofd, 0); if (addr == MAP_FAILED) err(1, "ro mmap"); if (memcmp(addr, "bubu", 4) == 0) errx(1, "identical startup data"); rwfd = open(argv[1], O_WRONLY); if (rwfd == -1) err(1, "rw open"); ret = write(rwfd, "bubu", 4); if (ret == -1) err(1, "write"); if (ret < 4) errx(1, "short write"); if (memcmp(addr, "bubu", 4) != 0) errx(1, "bad mmap data"); ret = read(rofd, buf, 4); if (ret == -1) err(1, "read"); if (ret < 4) errx(1, "short read"); if (memcmp(buf, "bubu", 4) != 0) errx(1, "bad read data"); return 0; } EOF gcc -o rorw-map rorw-map.c mkdir -p mnt lower upper work echo baba > lower/foo mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work mnt ./rorw-map mnt/foo umount mnt - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - - No output means success, "rorw-map: bad mmap data" means failure. Signed-off-by: Miklos Szeredi --- fs/overlayfs/inode.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index 09c6f99bd5db..25b31c6ebe9e 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -11,6 +11,7 @@ #include #include #include +#include #include #include #include @@ -392,6 +393,25 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *to) return ret; } +static int ovl_mmap(struct file *file, struct vm_area_struct *vma) +{ + if (likely(ovl_file_is_lower(file))) + return OVL_CALL_REAL_FOP(file, mmap(file, vma)); + + file = filp_clone_open(file); + if (IS_ERR(file)) + return PTR_ERR(file); + + fput(vma->vm_file); + /* transfer ref: */ + vma->vm_file = file; + + if (!file->f_op->mmap) + return -ENODEV; + + return file->f_op->mmap(file, vma); +} + static struct ovl_fops *ovl_fops_find(const struct file_operations *orig) { struct ovl_fops *ofop; @@ -431,9 +451,10 @@ static struct ovl_fops *ovl_fops_get(struct file *file) /* Intercept these: */ if (orig->read_iter) ofop->fops.read_iter = ovl_read_iter; + if (orig->mmap) + ofop->fops.mmap = ovl_mmap; /* These will need to be intercepted: */ - ofop->fops.mmap = orig->mmap; ofop->fops.fsync = orig->fsync; /* -- 2.5.5