Assembly call bash command with argv[]

Question

I am very new to assembly and I am trying to call:

/bin/bash -c "echo hello; ls -la"

I store the "/bin/bash" command as a string and its address in RBX and RDI. 59 on RAX for the execve syscall that I perform at the end. -c on RSI as the second argument with the echo line on the third. Here's what gdb sees on the registers before the syscall line.

RBX: 0x4000b3 ("/bin/bash")
RCX: 0x0 
RDX: 0x4000c8 ("\"echo hello; ls -la\"")
RSI: 0x4000c5 --> 0x6f6863652200632d ('-c')
RDI: 0x4000b3 ("/bin/bash")
RBP: 0x0 
RSP: 0x7fffffffe0e0 --> 0x1 
RIP: 0x4000a7 --> 0xe8050f0000003bb8

But when I start the executable nothing happens. I thought the registers are used for the argv[] arguments.

I debugged the program and I honestly can't tell what's going wrong but then again I am really new so maybe I am not actually giving the arguments to the syscall?

There should be a single register that contains the address of the argv array. That should be an array of pointers to the individual arguments. And make sure that argv[0] contains "bash" or "/bin/bash" — Barmar
– Barmar, Commented Apr 23, 2024 at 20:48
The double-quotes shouldn't be part of the actual string. When you run /bin/bash -c "echo hello; ls -la" in bash or sh, the quotes protect that part of the command line from word-splitting, but quote-removal happens before passing that string to argv of the child process. Try it yourself with printf "%s\n" -c "hello world" 'hi mom' "quotes 'inside' quotes aren't removed" on a bash command line. — Peter Cordes
– Peter Cordes, Commented Apr 23, 2024 at 21:13
Anyway, look at the man page for execve, man7.org/linux/man-pages/man2/execve.2.html . RDI is const char *pathname, RSI is char *const argv[], a pointer to an array of pointers. — Peter Cordes
– Peter Cordes, Commented Apr 23, 2024 at 21:15
extending PeterCorde's comment with one further demonstration: printf "%s\n" ...... "quotes 'inside' quotes aren't removed" 'same "for dbls" inside singles' Good luck to all. — shellter
– shellter, Commented Apr 23, 2024 at 23:43

Noah · Accepted Answer · 2024-04-23 20:53:39Z

0

Try splitting the command string into seperate arguments and storing their addresses in memory. Also make sure that the last argument in both the "argv[]" and "envp[]" arrays is a NULL pointer to terminate the array.

answered Apr 23, 2024 at 20:53

Noah

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2 Comments

tjm3772 Over a year ago

Splitting the command string is wrong in the bash -c case. The entire command string needs to be a single argument, any arguments after it are treated as positional parameters.

tripleee Over a year ago

So the correct value for argv is ["bash\0", "-c\0", "echo hello; ls\0"]

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