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    Subject[PATCH 4.9 109/116] sg_write()/bsg_write() is not fit to be called under KERNEL_DS
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

    From: Al Viro <viro@zeniv.linux.org.uk>

    commit 128394eff343fc6d2f32172f03e24829539c5835 upstream.

    Both damn things interpret userland pointers embedded into the payload;
    worse, they are actually traversing those. Leaving aside the bad
    API design, this is very much _not_ safe to call with KERNEL_DS.
    Bail out early if that happens.

    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    block/bsg.c | 3 +++
    drivers/scsi/sg.c | 3 +++
    2 files changed, 6 insertions(+)

    --- a/block/bsg.c
    +++ b/block/bsg.c
    @@ -655,6 +655,9 @@ bsg_write(struct file *file, const char

    dprintk("%s: write %Zd bytes\n", bd->name, count);

    + if (unlikely(segment_eq(get_fs(), KERNEL_DS)))
    + return -EINVAL;
    +
    bsg_set_block(bd, file);

    bytes_written = 0;
    --- a/drivers/scsi/sg.c
    +++ b/drivers/scsi/sg.c
    @@ -581,6 +581,9 @@ sg_write(struct file *filp, const char _
    sg_io_hdr_t *hp;
    unsigned char cmnd[SG_MAX_CDB_SIZE];

    + if (unlikely(segment_eq(get_fs(), KERNEL_DS)))
    + return -EINVAL;
    +
    if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
    return -ENXIO;
    SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp,

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