I had to use ed once in a very limited recovery situation. I don't remember the details but even vi was not an option. It's not terrible if you just need to change a few lines. Using it on a teletype to write code all day would get tedious quickly. Full-screen editors had to have been an amazing productivity boost.
I think ed is still a great editor for specific tasks. As a plan 9/9front user, when you get yourself into trouble, it's sometimes the only editor you've got left (like when graphics doesn't initialize, which I've not seen on 9front — ever?)
It's really not bad, and you can use it for scripting like sed, but it's clunkier.
I had to use it when I installed 9front on a computer that has no graphics card just a serial port (APU2C2). I had only a serial device at 9600bps and the other text editors (sam, acme) didn't worked. I wanted to turn it into a CPU server so I can use drawterm to access it remotely and that requires editing a few files.
I’m guessing v4 C didn’t have structs yet (v6 C does, but struct members are actually in the global namespace and are basically just sugar for offset and a type cast; member access even worked on literals. That’s why structs from early unix APIs have prefixed member names, like st_mode.
There may have been a early C without structs (B had none,) but according to Ken Thompson, the addition of structs to C was an important change, and a reason why his third attempt rewrite UNIX from assembly to a portable language finally succeeded. Certainly by the time the recently recovered v4 tape was made, C had structs:
~/unix_v4$ cat usr/sys/proc.h
struct proc {
char p_stat;
char p_flag;
char p_pri;
char p_sig;
char p_null;
char p_time;
int p_ttyp;
int p_pid;
int p_ppid;
int p_addr;
int p_size;
int p_wchan;
int *p_textp;
} proc[NPROC];
/* stat codes */
#define SSLEEP 1
#define SWAIT 2
#define SRUN 3
#define SIDL 4
#define SZOMB 5
/* flag codes */
#define SLOAD 01
#define SSYS 02
#define SLOCK 04
#define SSWAP 010
You don't actually need i here. i is the same as (q - password). It would be idiomatic C to simply rewrite the loop condition as: while (q < password+sizeof(password) && (*q = getchar()) != '\n'). To preserve your "goto error;" part, maybe you could do the overflow check when null terminating outside the loop.
Isn't sizeof only standardised in C89? Wouldn't shock me if this form needs to be an rvalue.
The author did try pointer arithmetic:
> I initially attempted a fix using pointer arithmetic, but the 1973 C compiler didn’t like it, while it didn’t refuse the syntax, the code had no effect.
Back in the 80s, when I was writing a C compiler, C compilers typically had a maximum size for string literals. The behavior was to detect overflow, issue an error message, and fail compilation.
I took a different tack. The buffer was allocated with malloc. When a string was larger, it was realloced to a larger size. This worked until memory was exhausted, and then the program quit.
It was actually less code to implement than having a fixed size buffer.
Ditto for the other compilation limits, such as length of a line. The only limit was running out of memory.
so, is there already somebody that wrote the exploit for it? are there any special things to consider exploiting such architecture back in the day or do the same basic principles apply?
perhaps the downvoters can tell me why they are downvoting? i'm curious to hear whether if this would work on unix v4 or whether there are special things to consider. I thought i would ask claude for a basic example so people could perhaps provide feedback. i guess people consider it low effort reply? anyway, thanks for your input.
The password and pwbuf arrays are declared one right after the other. Will they appear consecutive in memory, i.e. will you overwrite pwbuf when writing past password?
If so, could you type the same password that’s exactly 100 bytes twice and then hit enter to gain root? With only clobbering one additional byte, of ttybuf?
Edit: no, silly, password is overwritten with its hash before the comparison.
> will you overwrite pwbuf when writing past password?
Right.
> If so, could you type the same password that’s exactly 100 bytes twice and then hit enter to gain root? With only clobbering one additional byte, of ttybuf?
Almost. You need to type crypt(password) in the part that overflows to pwbuf.
I had to use ed once in a very limited recovery situation. I don't remember the details but even vi was not an option. It's not terrible if you just need to change a few lines. Using it on a teletype to write code all day would get tedious quickly. Full-screen editors had to have been an amazing productivity boost.
I think ed is still a great editor for specific tasks. As a plan 9/9front user, when you get yourself into trouble, it's sometimes the only editor you've got left (like when graphics doesn't initialize, which I've not seen on 9front — ever?)
It's really not bad, and you can use it for scripting like sed, but it's clunkier.
ed makes a lot more sense if you remember they were printing everything to paper rather than using a glass tty when it was first developed
I had to use it when I installed 9front on a computer that has no graphics card just a serial port (APU2C2). I had only a serial device at 9600bps and the other text editors (sam, acme) didn't worked. I wanted to turn it into a CPU server so I can use drawterm to access it remotely and that requires editing a few files.
The amount of code was relatively low.
Not the million line codebases we have today. 50-100 lines was the usual program or script.
iirc they were initially using actual ttys(as in typewriters) and the input delay was hell which is the reason so many UNIX commands are two letters.
So likely they would work on the printout:
And then input the corrections into ed(1).
1 reply →
What is up with fin? Is it really just writing an int 0 in the memory right after some variable present in libc or similar?
Predecessor of
I’m guessing v4 C didn’t have structs yet (v6 C does, but struct members are actually in the global namespace and are basically just sugar for offset and a type cast; member access even worked on literals. That’s why structs from early unix APIs have prefixed member names, like st_mode.
> I’m guessing v4 C didn’t have structs yet
There may have been a early C without structs (B had none,) but according to Ken Thompson, the addition of structs to C was an important change, and a reason why his third attempt rewrite UNIX from assembly to a portable language finally succeeded. Certainly by the time the recently recovered v4 tape was made, C had structs:
)
1 reply →
According to the chatbot, the first word of `fin` is the file descriptor, the second its state. "Reset stdin’s flags to a clean state".
A bit of a code review (some details from the patch removed for clarity):
You don't actually need i here. i is the same as (q - password). It would be idiomatic C to simply rewrite the loop condition as: while (q < password+sizeof(password) && (*q = getchar()) != '\n'). To preserve your "goto error;" part, maybe you could do the overflow check when null terminating outside the loop.
Isn't sizeof only standardised in C89? Wouldn't shock me if this form needs to be an rvalue.
The author did try pointer arithmetic:
> I initially attempted a fix using pointer arithmetic, but the 1973 C compiler didn’t like it, while it didn’t refuse the syntax, the code had no effect.
This surprised me too. The snippet I was quoting from was already using sizeof, though.
I missed the blurb about pointer arithmetic. Would be interesting to go into detail about what "had no effect" means.
Back in the 80s, when I was writing a C compiler, C compilers typically had a maximum size for string literals. The behavior was to detect overflow, issue an error message, and fail compilation.
I took a different tack. The buffer was allocated with malloc. When a string was larger, it was realloced to a larger size. This worked until memory was exhausted, and then the program quit.
It was actually less code to implement than having a fixed size buffer.
Ditto for the other compilation limits, such as length of a line. The only limit was running out of memory.
so, is there already somebody that wrote the exploit for it? are there any special things to consider exploiting such architecture back in the day or do the same basic principles apply?
Yeah, somebody came up with one here: https://news.ycombinator.com/item?id=46469897
EDIT: removed due to low effort and mark-up issues. thank you all for your feedback.
perhaps the downvoters can tell me why they are downvoting? i'm curious to hear whether if this would work on unix v4 or whether there are special things to consider. I thought i would ask claude for a basic example so people could perhaps provide feedback. i guess people consider it low effort reply? anyway, thanks for your input.
7 replies →
Are you sure any buffer overflows were actually fixed in 1973?
The password and pwbuf arrays are declared one right after the other. Will they appear consecutive in memory, i.e. will you overwrite pwbuf when writing past password?
If so, could you type the same password that’s exactly 100 bytes twice and then hit enter to gain root? With only clobbering one additional byte, of ttybuf?
Edit: no, silly, password is overwritten with its hash before the comparison.
> will you overwrite pwbuf when writing past password?
Right.
> If so, could you type the same password that’s exactly 100 bytes twice and then hit enter to gain root? With only clobbering one additional byte, of ttybuf?
Almost. You need to type crypt(password) in the part that overflows to pwbuf.
Already patched this on my x86_64 v4 UNIX port. Hehe.
That sounds really fun!
> x86_64 v4 UNIX port
What compiler are you using?
gcc. Im also working on a port of the original compiler, but that's a much lower priority for me.
Having a buffer with a fixed size is always a red flag for further checking.
Related:
An initial analysis of the discovered Unix V4 tape
https://news.ycombinator.com/item?id=46468283
The source has
ttybuf[2] =& ~010;
Which is another bug.
What's the bug? If you're referring to the =& syntax, then that's just how &= used to be written in older versions of C.
Remotely exploiting a buffer overflow in Unix like it's 1973.
# ... sound of crickets ...
Wanna see me do it again?
Remotely? ... this version of UNIX doesn't have any networking.