From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: [PATCH 9/9] overlayfs: Append MAY_READ when diluting write checks Date: Wed, 13 Jul 2016 10:44:55 -0400 Message-ID: <1468421095-22322-10-git-send-email-vgoyal@redhat.com> References: <1468421095-22322-1-git-send-email-vgoyal@redhat.com> Return-path: In-Reply-To: <1468421095-22322-1-git-send-email-vgoyal@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: miklos@szeredi.hu, sds@tycho.nsa.gov, pmoore@redhat.com, casey@schaufler-ca.com, linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org, linux-security-module@vger.kernel.org Cc: dwalsh@redhat.com, dhowells@redhat.com, viro@ZenIV.linux.org.uk, vgoyal@redhat.com, linux-fsdevel@vger.kernel.org List-Id: linux-unionfs@vger.kernel.org Right now we remove MAY_WRITE/MAY_APPEND bits from mask if realfile is on lower/. This is done as files on lower will never be written and will be copied up. But to copy up a file, mounter should have MAY_READ permission otherwise copy up will fail. So set MAY_READ in mask when MAY_WRITE is reset. Dan Walsh noticed this when he did access(lowerfile, W_OK) and it returned True (context mounts) but when he tried to actually write to file, it failed as mounter did not have permission on lower file. Reported-by: Dan Walsh Signed-off-by: Vivek Goyal --- fs/overlayfs/inode.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index 6d9d86e..83b2422 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -140,8 +140,13 @@ int ovl_permission(struct inode *inode, int mask) return err; old_cred = ovl_override_creds(inode->i_sb); - if (!is_upper && !special_file(realinode->i_mode)) - mask &= ~(MAY_WRITE | MAY_APPEND); + if (!is_upper && !special_file(realinode->i_mode)) { + if (mask & MAY_WRITE || mask & MAY_APPEND) { + mask &= ~(MAY_WRITE | MAY_APPEND); + /* Make sure mounter can read file for copy up later */ + mask |= MAY_READ; + } + } err = inode_permission(realinode, mask); revert_creds(old_cred); -- 2.7.4