From: Kees Cook
Sent: 11 August 2023 06:46
If an output buffer size exceeded U16_MAX, the min_t(u16, ...) cast in copy_data() was causing writes to truncate. This manifested as output bytes being skipped, seen as %NUL bytes in pstore dumps when the available record size was larger than 65536. Fix the cast to no longer truncate the calculation.
...
diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c index 2dc4d5a1f1ff..fde338606ce8 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -1735,7 +1735,7 @@ static bool copy_data(struct prb_data_ring *data_ring, if (!buf || !buf_size) return true;
- data_size = min_t(u16, buf_size, len);
- data_size = min_t(unsigned int, buf_size, len);
I'd noticed that during one of my test compiles while looking at making min() less fussy.
A better fix would be: data_size = min(buf_size + 0u, len);
Or put an ack on my patch 3/5 to minmax.h and then min(buf_size, len) will be fine (because both arguments are unsigned).
David
memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */ return true; -- 2.34.1
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