fingerd

Repair this code

Repair the copy so it never writes past the buffer, truncating and null terminating within cap.

today's brief

November 2, 1988. A Cornell grad student named Robert Morris releases a worm that spreads through, among other holes, the finger service, which read a network request into a fixed 512 byte buffer using gets, with no length check at all. Overrun the buffer and you owned the machine. The worm reinfected so hard it ground about ten percent of the internet to a halt overnight, and it led to the first felony conviction under the US computer fraud law. Copy into the buffer, but stop at its edge.

See it in action

safe_copy(dst, 512, "hi")

Expected result

2 (dst is "hi")

Your checklist

For your own tracking. Tests grade your code.

Copy src into dst, but write at most cap characters total, including the terminating zero.
Null terminate dst, and return the number of characters copied (not counting the zero).
The starter copies the whole string with no bounds check, exactly the gets bug. Add the limit.

More examples

safe_copy(dst, 4, "hello")

Expected result

3 (dst is "hel")

Constraints

Expected files

copy.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions

fingerd

Repair this code

Repair the copy so it never writes past the buffer, truncating and null terminating within cap.

today's brief

See it in action

safe_copy(dst, 512, "hi")

Expected result

2 (dst is "hi")

Your checklist

For your own tracking. Tests grade your code.

Copy src into dst, but write at most cap characters total, including the terminating zero.
Null terminate dst, and return the number of characters copied (not counting the zero).
The starter copies the whole string with no bounds check, exactly the gets bug. Add the limit.

More examples

safe_copy(dst, 4, "hello")

Expected result

3 (dst is "hel")

Constraints

Expected files

copy.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions