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    Subject[PATCH 3.18 07/15] ALSA: info: Check for integer overflow in snd_info_entry_write()
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

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

    From: Erick Reyes <erickreyes@google.com>

    Commit 4adb7bcbcb69 ("ALSA: core: Use seq_file for text proc file
    reads") heavily refactored ALSA procfs and fixed the overflow as
    a side-effect, so this fix only applies to kernels < 4.2 and
    there is no upstream equivalent

    snd_info_entry_write() resizes the buffer with an unsigned long
    size argument that gets truncated because resize_info_buffer()
    takes the size parameter as an unsigned int. On 64-bit kernels,
    this causes the following copy_to_user() to write out-of-bounds
    if (pos + count) can't be represented by an unsigned int.

    Signed-off-by: Siqi Lin <siqilin@google.com>
    Signed-off-by: Erick Reyes <erickreyes@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    sound/core/info.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/sound/core/info.c
    +++ b/sound/core/info.c
    @@ -253,6 +253,7 @@ static ssize_t snd_info_entry_write(stru
    struct snd_info_buffer *buf;
    ssize_t size = 0;
    loff_t pos;
    + unsigned long realloc_size;

    data = file->private_data;
    if (snd_BUG_ON(!data))
    @@ -261,7 +262,8 @@ static ssize_t snd_info_entry_write(stru
    pos = *offset;
    if (pos < 0 || (long) pos != pos || (ssize_t) count < 0)
    return -EIO;
    - if ((unsigned long) pos + (unsigned long) count < (unsigned long) pos)
    + realloc_size = (unsigned long) pos + (unsigned long) count;
    + if (realloc_size < (unsigned long) pos || realloc_size > UINT_MAX)
    return -EIO;
    switch (entry->content) {
    case SNDRV_INFO_CONTENT_TEXT:

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