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    Subject[PATCH] sound/oss/midi_synth: prevent underflow, use of uninitialized value, and signedness issue
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    The offset passed to midi_synth_load_patch() can be essentially
    arbitrary. If it's greater than the header length, this will result in
    a copy_from_user(dst, src, negative_val). While this will just return
    -EFAULT on x86, on other architectures this may cause memory corruption.
    Additionally, the length field of the sysex_info structure may not be
    initialized prior to its use. Finally, a signed comparison may result
    in an unintentionally large loop.

    This patch fixes all these issues, as well as some cleanup to prevent
    checkpatch.pl from complaining.

    Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
    Cc: stable@kernel.org
    ---
    sound/oss/midi_synth.c | 27 ++++++++++++++-------------
    1 files changed, 14 insertions(+), 13 deletions(-)

    diff --git a/sound/oss/midi_synth.c b/sound/oss/midi_synth.c
    index 3c09374..3500f80 100644
    --- a/sound/oss/midi_synth.c
    +++ b/sound/oss/midi_synth.c
    @@ -491,16 +491,18 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,
    if (!prefix_cmd(orig_dev, 0xf0))
    return 0;

    + /* Invalid patch format */
    if (format != SYSEX_PATCH)
    - {
    -/* printk("MIDI Error: Invalid patch format (key) 0x%x\n", format);*/
    return -EINVAL;
    - }
    +
    + /* Patch header too short */
    if (count < hdr_size)
    - {
    -/* printk("MIDI Error: Patch header too short\n");*/
    return -EINVAL;
    - }
    +
    + /* Offset too high */
    + if (offs > offsetof(struct sysex_info, len) || offs < 0)
    + return -EINVAL;
    +
    count -= hdr_size;

    /*
    @@ -510,14 +512,13 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,

    if(copy_from_user(&((char *) &sysex)[offs], &(addr)[offs], hdr_size - offs))
    return -EFAULT;
    -
    - if (count < sysex.len)
    - {
    -/* printk(KERN_WARNING "MIDI Warning: Sysex record too short (%d<%d)\n", count, (int) sysex.len);*/
    +
    + /* Sysex record too short */
    + if ((unsigned)count < (unsigned)sysex.len)
    sysex.len = count;
    - }
    - left = sysex.len;
    - src_offs = 0;
    +
    + left = sysex.len;
    + src_offs = 0;

    for (i = 0; i < left && !signal_pending(current); i++)
    {



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