4.19-stable review patch. If anyone has any objections, please let me know.
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From: Lee Jones lee@kernel.org
[ Upstream commit 86b20af11e84c26ae3fde4dcc4f490948e3f8035 ]
There is a general misunderstanding amongst engineers that {v}snprintf() returns the length of the data *actually* encoded into the destination array. However, as per the C99 standard {v}snprintf() really returns the length of the data that *would have been* written if there were enough space for it. This misunderstanding has led to buffer-overruns in the past. It's generally considered safer to use the {v}scnprintf() variants in their place (or even sprintf() in simple cases). So let's do that.
Whilst we're at it, let's define some magic numbers to increase readability and ease of maintenance.
Link: https://lwn.net/Articles/69419/ Link: https://github.com/KSPP/linux/issues/105 Cc: Tomoki Sekiyama tomoki.sekiyama@gmail.com Signed-off-by: Lee Jones lee@kernel.org Link: https://lore.kernel.org/r/20231213164246.1021885-9-lee@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Stable-dep-of: 93907620b308 ("USB: misc: yurex: fix race between read and write") Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/usb/misc/yurex.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c index 08b72bb22b7ef..a85cc0f3e15c4 100644 --- a/drivers/usb/misc/yurex.c +++ b/drivers/usb/misc/yurex.c @@ -34,6 +34,8 @@ #define YUREX_BUF_SIZE 8 #define YUREX_WRITE_TIMEOUT (HZ*2)
+#define MAX_S64_STRLEN 20 /* {-}922337203685477580{7,8} */ + /* table of devices that work with this driver */ static struct usb_device_id yurex_table[] = { { USB_DEVICE(YUREX_VENDOR_ID, YUREX_PRODUCT_ID) }, @@ -402,7 +404,7 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count, { struct usb_yurex *dev; int len = 0; - char in_buffer[20]; + char in_buffer[MAX_S64_STRLEN]; unsigned long flags;
dev = file->private_data; @@ -413,14 +415,14 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count, return -ENODEV; }
+ if (WARN_ON_ONCE(dev->bbu > S64_MAX || dev->bbu < S64_MIN)) + return -EIO; + spin_lock_irqsave(&dev->lock, flags); - len = snprintf(in_buffer, 20, "%lld\n", dev->bbu); + scnprintf(in_buffer, MAX_S64_STRLEN, "%lld\n", dev->bbu); spin_unlock_irqrestore(&dev->lock, flags); mutex_unlock(&dev->io_mutex);
- if (WARN_ON_ONCE(len >= sizeof(in_buffer))) - return -EIO; - return simple_read_from_buffer(buffer, count, ppos, in_buffer, len); }