On Fri, Jul 13, 2018 at 12:29:36AM +0200, Jann Horn wrote:
> From: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
>
> From: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
>
> 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.
Or you could try this (completely untested, though):
diff --git a/drivers/staging/speakup/speakup_soft.c b/drivers/staging/speakup/speakup_soft.c
index a61bc41b82d7..198936ed0b54 100644
--- a/drivers/staging/speakup/speakup_soft.c
+++ b/drivers/staging/speakup/speakup_soft.c
@@ -192,13 +192,10 @@ static int softsynth_close(struct inode *inode, struct file *fp)
return 0;
}
-static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count,
- loff_t *pos, int unicode)
+static ssize_t softsynthx_read_iter(struct kiocb *iocb, struct iov_iter *to, int unicode)
{
int chars_sent = 0;
- char __user *cp;
char *init;
- u16 ch;
int empty;
unsigned long flags;
DEFINE_WAIT(wait);
@@ -211,7 +208,7 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count,
if (!synth_buffer_empty() || speakup_info.flushing)
break;
spin_unlock_irqrestore(&speakup_info.spinlock, flags);
- if (fp->f_flags & O_NONBLOCK) {
+ if (iocb->ki_flags & IOCB_NOWAIT) {
finish_wait(&speakup_event, &wait);
return -EAGAIN;
}
@@ -224,11 +221,14 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count,
}
finish_wait(&speakup_event, &wait);
- cp = buf;
init = get_initstring();
/* Keep 3 bytes available for a 16bit UTF-8-encoded character */
- while (chars_sent <= count - 3) {
+ while (iov_iter_count(to)) {
+ u_char s[3];
+ int l, n;
+ u16 ch;
+
if (speakup_info.flushing) {
speakup_info.flushing = 0;
ch = '\x18';
@@ -244,60 +244,47 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count,
spin_unlock_irqrestore(&speakup_info.spinlock, flags);
if ((!unicode && ch < 0x100) || (unicode && ch < 0x80)) {
- u_char c = ch;
-
- if (copy_to_user(cp, &c, 1))
- return -EFAULT;
-
- chars_sent++;
- cp++;
+ s[0] = ch;
+ l = 1;
} else if (unicode && ch < 0x800) {
- u_char s[2] = {
- 0xc0 | (ch >> 6),
- 0x80 | (ch & 0x3f)
- };
-
- if (copy_to_user(cp, s, sizeof(s)))
- return -EFAULT;
-
- chars_sent += sizeof(s);
- cp += sizeof(s);
+ s[0] = 0xc0 | (ch >> 6);
+ s[1] = 0x80 | (ch & 0x3f);
+ l = 2;
} else if (unicode) {
- u_char s[3] = {
- 0xe0 | (ch >> 12),
- 0x80 | ((ch >> 6) & 0x3f),
- 0x80 | (ch & 0x3f)
- };
-
- if (copy_to_user(cp, s, sizeof(s)))
- return -EFAULT;
-
- chars_sent += sizeof(s);
- cp += sizeof(s);
+ s[0] = 0xe0 | (ch >> 12);
+ s[1] = 0x80 | ((ch >> 6) & 0x3f);
+ s[2] = 0x80 | (ch & 0x3f);
+ l = 3;
}
-
+ n = copy_to_iter(s, l, to);
+ if (n != l) {
+ iov_iter_revert(to, n);
+ spin_lock_irqsave(&speakup_info.spinlock, flags);
+ break;
+ }
+ chars_sent += l;
spin_lock_irqsave(&speakup_info.spinlock, flags);
}
- *pos += chars_sent;
+ iocb->ki_pos += chars_sent;
empty = synth_buffer_empty();
spin_unlock_irqrestore(&speakup_info.spinlock, flags);
if (empty) {
speakup_start_ttys();
- *pos = 0;
+ iocb->ki_pos = 0;
}
return chars_sent;
}
-static ssize_t softsynth_read(struct file *fp, char __user *buf, size_t count,
+static ssize_t softsynth_read_iter(struct kiocb *iocb, struct iov_iter *to)
loff_t *pos)
{
- return softsynthx_read(fp, buf, count, pos, 0);
+ return softsynthx_read_iter(iocb, to, 0);
}
-static ssize_t softsynthu_read(struct file *fp, char __user *buf, size_t count,
+static ssize_t softsynthu_read_iter(struct kiocb *iocb, struct iov_iter *to)
loff_t *pos)
{
- return softsynthx_read(fp, buf, count, pos, 1);
+ return softsynthx_read_iter(iocb, to, 1);
}
static int last_index;
@@ -343,7 +330,7 @@ static unsigned char get_index(struct spk_synth *synth)
static const struct file_operations softsynth_fops = {
.owner = THIS_MODULE,
.poll = softsynth_poll,
- .read = softsynth_read,
+ .read_iter = softsynth_read_iter,
.write = softsynth_write,
.open = softsynth_open,
.release = softsynth_close,
@@ -352,7 +339,7 @@ static const struct file_operations softsynth_fops = {
static const struct file_operations softsynthu_fops = {
.owner = THIS_MODULE,
.poll = softsynth_poll,
- .read = softsynthu_read,
+ .read_iter = softsynthu_read_iter,
.write = softsynth_write,
.open = softsynth_open,
.release = softsynth_close,
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