The atomicity violation issue is due to the invalidation of the function port_has_data()'s check caused by concurrency. Imagine a scenario where a port that contains data passes the validity check but is simultaneously assigned a value with no data. This could result in an empty port passing the validity check, potentially leading to a null pointer dereference error later in the program, which is inconsistent.

To address this issue, we added a separate validity check for the variable buf after its assignment. This ensures that an invalid buf does not proceed further into the program, thereby preventing a null pointer dereference error.

This possible bug is found by an experimental static analysis tool developed by our team. This tool analyzes the locking APIs to extract function pairs that can be concurrently executed, and then analyzes the instructions in the paired functions to identify possible concurrency bugs including data races and atomicity violations.

Fixes: 203baab8ba31 ("virtio: console: Introduce function to hand off data from host to readers") Cc: stable@vger.kernel.org Signed-off-by: Qiu-ji Chen chenqiuji666@gmail.com --- V2: The logic of the fix has been modified. --- drivers/char/virtio_console.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c index c62b208b42f1..54fee192d93c 100644 --- a/drivers/char/virtio_console.c +++ b/drivers/char/virtio_console.c @@ -660,6 +660,10 @@ static ssize_t fill_readbuf(struct port *port, u8 __user *out_buf, return 0;

buf = port->inbuf; + + if (!buf) + return 0; + out_count = min(out_count, buf->len - buf->offset);

if (to_user) {