[PATCH] Missing BKL in sys_chroot() for 2.6

From: BlaisorBlade (blaisorblade_spam_at_yahoo.it)
Date: 06/06/04

  • Next message: Anil: "RE: [PATCH] speedup flush_workqueue for singlethread_workqueue" 
    To: Andrew Morton <akpm@osdl.org>, Linus Torvalds <torvalds@osdl.org>
Date:	Sun, 6 Jun 2004 19:58:48 +0200

    (PLEASE cc me on replies as I'm not subscribed).

    Set_fs_root *claims* it wants the BKL held:

    /*
     * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
     * It can block. Requires the big lock held.
     */
    void set_fs_root(struct fs_struct *fs, struct vfsmount *mnt,
                     struct dentry *dentry)

    But sys_chroot ignores this. So I attach this patch (apply with patch -p1 -l).
    Maybe the solution is to kill that comment, maybe not (sys_pivot_root() calls
    chroot_fs_refs() -> set_fs_root() with the BKL held, but that has a lot of
    reasons other than this). If that comment is correct, however, it probably
    holds even for set_fs_altroot(), since it's similar. So this patch adds it.

    TESTING: none, I'm sure about the inconsistency, a lot less about the solution
    (no kernel manual explains the BKL, since it is a relict; except the ones who
    still says it blocks all the rest of the kernel, while I think it is just a
    recursive and "sleepable" spinlock - am I correct?).

    --- vanilla-linux-2.6.6/fs/open.c.saved 2004-05-10 21:37:11.000000000 +0200
    +++ vanilla-linux-2.6.6/fs/open.c 2004-06-06 19:40:20.000000000 +0200
    @@ -581,8 +581,13 @@
            if (!capable(CAP_SYS_CHROOT))
                    goto dput_and_out;

    + lock_kernel();
    +
            set_fs_root(current->fs, nd.mnt, nd.dentry);
            set_fs_altroot();
    +
    + unlock_kernel();
    +
            error = 0;
     dput_and_out:
            path_release(&nd);
    --- vanilla-linux-2.6.6/fs/namei.c.saved 2004-05-10 21:37:09.000000000
    +0200
    +++ vanilla-linux-2.6.6/fs/namei.c 2004-06-06 19:49:25.000000000 +0200
    @@ -814,6 +814,9 @@
            return 1;
     }

    +/*
    + * Requires the big lock held.
    + */
     void set_fs_altroot(void)
     {
            char *emul = __emul_prefix(); 

    -- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
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