• Steven Rostedt (Red Hat)'s avatar
    seq_buf: Fix seq_buf_bprintf() truncation · 4d4eb4d4
    Steven Rostedt (Red Hat) authored
    In seq_buf_bprintf(), bstr_printf() is used to copy the format into the
    buffer remaining in the seq_buf structure. The return of bstr_printf()
    is the amount of characters written to the buffer excluding the '\0',
    unless the line was truncated!
    
    If the line copied does not fit, it is truncated, and a '\0' is added
    to the end of the buffer. But in this case, '\0' is included in the length
    of the line written. To know if the buffer had overflowed, the return
    length will be the same or greater than the length of the buffer passed in.
    
    The check in seq_buf_bprintf() only checked if the length returned from
    bstr_printf() would fit in the buffer, as the seq_buf_bprintf() is only
    to be an all or nothing command. It either writes all the string into
    the seq_buf, or none of it. If the string is truncated, the pointers
    inside the seq_buf must be reset to what they were when the function was
    called. This is not the case. On overflow, it copies only part of the string.
    
    The fix is to change the overflow check to see if the length returned from
    bstr_printf() is less than the length remaining in the seq_buf buffer, and not
    if it is less than or equal to as it currently does. Then seq_buf_bprintf()
    will know if the write from bstr_printf() was truncated or not.
    
    Link: http://lkml.kernel.org/r/1425500481.2712.27.camel@perches.com
    
    Cc: stable@vger.kernel.org
    Reported-by: default avatarJoe Perches <joe@perches.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    4d4eb4d4
seq_buf.c 7.81 KB