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    Subject[PATCH AUTOSEL 5.7 319/388] ovl: verify permissions in ovl_path_open()
    Date
    From: Miklos Szeredi <mszeredi@redhat.com>

    [ Upstream commit 56230d956739b9cb1cbde439d76227d77979a04d ]

    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: Sasha Levin <sashal@kernel.org>
    ---
    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 36b60788ee47..a0878039332a 100644
    --- a/fs/overlayfs/util.c
    +++ b/fs/overlayfs/util.c
    @@ -459,7 +459,32 @@ 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 */
    --
    2.25.1
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