From: Miklos Szeredi mszeredi@redhat.com
mainline inclusion from mainline-v5.8-rc1 commit 56230d956739b9cb1cbde439d76227d77979a04d category: bugfix bugzilla: NA CVE: CVE-2020-16120
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Check permission before opening a real file.
ovl_path_open() is used by readdir and copy-up routines.
ovl_permission() theoretically already checked copy up permissions, but it doesn't hurt to re-do these checks during the actual copy-up.
For directory reading ovl_permission() only checks access to topmost underlying layer. Readdir on a merged directory accesses layers below the topmost one as well. Permission wasn't checked for these layers.
Note: modifying ovl_permission() to perform this check would be far more complex and hence more bug prone. The result is less precise permissions returned in access(2). If this turns out to be an issue, we can revisit this bug.
Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com Reviewed-by: zhangyi (F) yi.zhang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- fs/overlayfs/util.c | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-)
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c index d0570ac2788b9..eb9411461b695 100644 --- a/fs/overlayfs/util.c +++ b/fs/overlayfs/util.c @@ -466,7 +466,32 @@ bool ovl_is_whiteout(struct dentry *dentry)
struct file *ovl_path_open(struct path *path, int flags) { - return dentry_open(path, flags | O_NOATIME, current_cred()); + struct inode *inode = d_inode(path->dentry); + int err, acc_mode; + + if (flags & ~(O_ACCMODE | O_LARGEFILE)) + BUG(); + + switch (flags & O_ACCMODE) { + case O_RDONLY: + acc_mode = MAY_READ; + break; + case O_WRONLY: + acc_mode = MAY_WRITE; + break; + default: + BUG(); + } + + err = inode_permission(inode, acc_mode | MAY_OPEN); + if (err) + return ERR_PTR(err); + + /* O_NOATIME is an optimization, don't fail if not permitted */ + if (inode_owner_or_capable(inode)) + flags |= O_NOATIME; + + return dentry_open(path, flags, current_cred()); }
/* Caller should hold ovl_inode->lock */