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    Subject[ 067/262] fs/proc: fix potential unregister_sysctl_table hang
    Date
    From: Greg KH <gregkh@linuxfoundation.org>

    3.5-stable review patch. If anyone has any objections, please let me know.

    ------------------

    From: Francesco Ruggeri <fruggeri@aristanetworks.com>

    commit 6bf6104573482570f7103d3e5ddf9574db43a363 upstream.

    The unregister_sysctl_table() function hangs if all references to its
    ctl_table_header structure are not dropped.

    This can happen sometimes because of a leak in proc_sys_lookup():
    proc_sys_lookup() gets a reference to the table via lookup_entry(), but
    it does not release it when a subsequent call to sysctl_follow_link()
    fails.

    This patch fixes this leak by making sure the reference is always
    dropped on return.

    See also commit 076c3eed2c31 ("sysctl: Rewrite proc_sys_lookup
    introducing find_entry and lookup_entry") which reorganized this code in
    3.4.

    Tested in Linux 3.4.4.

    Signed-off-by: Francesco Ruggeri <fruggeri@aristanetworks.com>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/proc/proc_sysctl.c | 5 ++---
    1 file changed, 2 insertions(+), 3 deletions(-)

    --- a/fs/proc/proc_sysctl.c
    +++ b/fs/proc/proc_sysctl.c
    @@ -462,9 +462,6 @@ static struct dentry *proc_sys_lookup(st

    err = ERR_PTR(-ENOMEM);
    inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
    - if (h)
    - sysctl_head_finish(h);
    -
    if (!inode)
    goto out;

    @@ -473,6 +470,8 @@ static struct dentry *proc_sys_lookup(st
    d_add(dentry, inode);

    out:
    + if (h)
    + sysctl_head_finish(h);
    sysctl_head_finish(head);
    return err;
    }



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