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    Subject[PATCH 3.19.y-ckt 094/164] proc: actually make proc_fd_permission() thread-friendly
    Date
    3.19.8-ckt11 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Oleg Nesterov <oleg@redhat.com>

    commit 54708d2858e79a2bdda10bf8a20c80eb96c20613 upstream.

    The commit 96d0df79f264 ("proc: make proc_fd_permission() thread-friendly")
    fixed the access to /proc/self/fd from sub-threads, but introduced another
    problem: a sub-thread can't access /proc/<tid>/fd/ or /proc/thread-self/fd
    if generic_permission() fails.

    Change proc_fd_permission() to check same_thread_group(pid_task(), current).

    Fixes: 96d0df79f264 ("proc: make proc_fd_permission() thread-friendly")
    Reported-by: "Jin, Yihua" <yihua.jin@intel.com>
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    fs/proc/fd.c | 14 +++++++++++---
    1 file changed, 11 insertions(+), 3 deletions(-)

    diff --git a/fs/proc/fd.c b/fs/proc/fd.c
    index 8e5ad83..4b724b3 100644
    --- a/fs/proc/fd.c
    +++ b/fs/proc/fd.c
    @@ -284,11 +284,19 @@ static struct dentry *proc_lookupfd(struct inode *dir, struct dentry *dentry,
    */
    int proc_fd_permission(struct inode *inode, int mask)
    {
    - int rv = generic_permission(inode, mask);
    + struct task_struct *p;
    + int rv;
    +
    + rv = generic_permission(inode, mask);
    if (rv == 0)
    - return 0;
    - if (task_tgid(current) == proc_pid(inode))
    + return rv;
    +
    + rcu_read_lock();
    + p = pid_task(proc_pid(inode), PIDTYPE_PID);
    + if (p && same_thread_group(p, current))
    rv = 0;
    + rcu_read_unlock();
    +
    return rv;
    }

    --
    1.9.1


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