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    Subject[PATCH 3.17 271/319] staging: comedi: fix memory leak / bad pointer freeing for chanlist
    Date
    3.17-stable review patch.  If anyone has any objections, please let me know.

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

    From: Ian Abbott <abbotti@mev.co.uk>

    commit 238b5ad855924919e5b98d0c772d9dc78795639b upstream.

    As a follow-up to commit 6cab7a37f5c04 ("staging: comedi: (regression)
    channel list must be set for COMEDI_CMD ioctl"), Hartley Sweeten pointed
    out another couple of bugs stemming from commit 6cab7a37f5c04 ("staging:
    comedi: comedi_fops: introduce __comedi_get_user_chanlist()").

    Firstly, `do_cmdtest_ioctl()` never frees the kernel copy of the user
    chanlist allocated by `__comedi_get_user_chanlist()`, so that memory is
    leaked. Fix it by freeing the allocated kernel memory pointed to by
    `cmd.chanlist` before that pointer is overwritten with its original
    pointer to user memory before `cmd` is copied back to user-space.

    Secondly, if `__comedi_get_user_chanlist()` returns an error,
    `cmd->chanlist` is left unchanged and in fact will be a pointer to user
    memory. This causes `do_cmd_ioctl()` to `goto cleanup` and call
    `do_become_nonbusy()` which would attempt to free the memory pointed to
    by the user-space pointer. Fix it by setting `cmd->chanlist` to NULL at
    the start of `__comedi_get_user_chanlist()`.

    Fixes: c6cd0eefb27b ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()")
    Reported-by: H Hartley Sweeten <hsweeten@visionengravers.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/staging/comedi/comedi_fops.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/drivers/staging/comedi/comedi_fops.c
    +++ b/drivers/staging/comedi/comedi_fops.c
    @@ -1462,6 +1462,7 @@ static int __comedi_get_user_chanlist(st
    unsigned int *chanlist;
    int ret;

    + cmd->chanlist = NULL;
    chanlist = memdup_user(user_chanlist,
    cmd->chanlist_len * sizeof(unsigned int));
    if (IS_ERR(chanlist))
    @@ -1615,6 +1616,8 @@ static int do_cmdtest_ioctl(struct comed

    ret = s->do_cmdtest(dev, s, &cmd);

    + kfree(cmd.chanlist); /* free kernel copy of user chanlist */
    +
    /* restore chanlist pointer before copying back */
    cmd.chanlist = (unsigned int __force *)user_chanlist;




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