4.17-stable review patch. If anyone has any objections, please let me know.
------------------ From: Samuel Thibault <[email protected]> commit b96fba8d5855c3617adbfb43ca4723a808cac954 upstream. If softsynthx_read() is called with `count < 3`, `count - 3` wraps, causing the loop to copy as much data as available to the provided buffer. If softsynthx_read() is invoked through sys_splice(), this causes an unbounded kernel write; but even when userspace just reads from it normally, a small size could cause userspace crashes. Fixes: 425e586cf95b ("speakup: add unicode variant of /dev/softsynth") Cc: [email protected] Signed-off-by: Samuel Thibault <[email protected]> Signed-off-by: Jann Horn <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- drivers/staging/speakup/speakup_soft.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/drivers/staging/speakup/speakup_soft.c +++ b/drivers/staging/speakup/speakup_soft.c @@ -197,11 +197,15 @@ static ssize_t softsynthx_read(struct fi int chars_sent = 0; char __user *cp; char *init; + size_t bytes_per_ch = unicode ? 3 : 1; u16 ch; int empty; unsigned long flags; DEFINE_WAIT(wait); + if (count < bytes_per_ch) + return -EINVAL; + spin_lock_irqsave(&speakup_info.spinlock, flags); while (1) { prepare_to_wait(&speakup_event, &wait, TASK_INTERRUPTIBLE); @@ -227,7 +231,7 @@ static ssize_t softsynthx_read(struct fi init = get_initstring(); /* Keep 3 bytes available for a 16bit UTF-8-encoded character */ - while (chars_sent <= count - 3) { + while (chars_sent <= count - bytes_per_ch) { if (speakup_info.flushing) { speakup_info.flushing = 0; ch = '\x18';
