[PATCH] evdev: fix evdev_write return value on partial writes

As was recently brought up on the busybox list
(http://lists.busybox.net/pipermail/busybox/2011-January/074565.html),
evdev_write doesn't properly check the count argument, which will
lead to a return value > count on partial writes if the remaining bytes
are accessible - Causing userspace confusion.

Fix it by only handling each full input_event structure, similar to how
it is done in evdev_read.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
---
 drivers/input/evdev.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index c8471a2..61fa24e 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c

@@ -330,7 +330,7 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer,
 		goto out;
 	}
 
-	while (retval < count) {
+	while ((retval + input_event_size()) <= count) {
 
 		if (input_event_from_user(buffer + retval, &event)) {
 			retval = -EFAULT;

-- 
1.7.2.3

Hi Peter,

On Thu, Jan 27, 2011 at 10:42:00AM +0100, Peter Korsgaard wrote:

As was recently brought up on the busybox list
(http://lists.busybox.net/pipermail/busybox/2011-January/074565.html),
evdev_write doesn't properly check the count argument, which will
lead to a return value > count on partial writes if the remaining bytes
are accessible - Causing userspace confusion.

Fix it by only handling each full input_event structure, similar to how
it is done in evdev_read.

A Reporte-by here would be nice.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

As I said on the Busybox list, applying this results in an endless

write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0

from the command

echo test > /dev/input/event0

write() should probably return -EINVAL here.

baruch

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