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unsigned int argc;
char *arg;
void **argv;
char *group;
int cmd_class;
int stash_index;
unsigned int stash_hash;
pr_table_t *notes;
int cmd_id;
int is_ftp;
const char *protocol;
} *
This structure holds all the attributes related to the command that is
going to be run on the server. Let's check the values of its members:
gef➤ p *cmd
$82 = {
pool = 0x5555556e0440,
server = 0x55555568ad28,
config = 0x5555556e0440,
tmp_pool = 0x0,
argc = 0x2,
arg = 0x5555556b9a98 "CCCwwwwww",
argv = 0x5555556b9ab8,
group = 0x0,
cmd_class = 0x67f,
stash_index = 0x14,
stash_hash = 0x3b7b88c,
notes = 0x5555556b9c28,
cmd_id = 0xffffffff,
is_ftp = 0x1,
protocol = 0x55555563c35f "FTP"
}
gef➤ p cmd
$82 = (cmd_rec *) 0x5555556b99f8
The array cmd->argv[] holds a pointer to our command. cmd->argv[0] holds
the command and cmd->argv[1] the arguments/parameters:
gef➤ x/s cmd->argv[0]
0x5555556b9a90: "3333"
gef➤ x/s cmd->argv[1]
0x5555556b9aa8: "CCCwwwwww"
This is defined in src/cmd.c at pr_cmd_alloc() function.
ProFTPd keeps a global variable called "session", which is responsible for
storing every attribute related to the current FTP session. The member
session.curr_cmd_rec holds a pointer to the current command being executed
in that FTP session. This is exactly the same value of cmd pointer in
_dispatch():
gef➤ p cmd
$82 = (cmd_rec *) 0x5555556b99f8
gef➤ p session.curr_cmd_rec
$83 = (struct cmd_struc *) 0x5555556b99f8
In addition, cmd has cmd->notes member that holds a pointer to a variable
of type struct table_rec (see src/table.c for more information).
Giving a couple of steps back, you may have noticed that when a breakpoint
is hit in pool.c:569, we are always pointing p->sub_next to some valid
address. This is because otherwise we would have a crash on sstrncpy()
like the one below:
$rax : 0x34
$rbx : 0x4343434343434344 ("DCCCCCCC"?)
$rcx : 0x0000555555688768 → 0x0000555500363234 ("426"?)
$rdx : 0x4343434343434343 ("CCCCCCCC"?)
$rsp : 0x00007fffffffd930 → 0x0000000000000008
$rbp : 0x00007fffffffd970 → 0x00007fffffffd9a0 → [...]
$rsi : 0x0000555555688768 → 0x0000555500363234 ("426"?)
$rdi : 0x4343434343434343 ("CCCCCCCC"?)
$rip : 0x0000555555634d28 → <sstrncpy+161> mov BYTE PTR [rdx], al
$r8 : 0x0000555555688738 → "Transfer aborted. Data connection closed"
[...]
─────────────────────────────────────────────────────────────── stack ────
0x00007fffffffd930│+0x0000: 0x0000000000000008 ← $rsp
0x00007fffffffd938│+0x0008: 0x0000000000000004
0x00007fffffffd940│+0x0010: 0x0000555555688769 → 0x5400005555003632 "26"
0x00007fffffffd948│+0x0018: 0x4343434343434343
0x00007fffffffd950│+0x0020: 0x00007fffffffd970 → [...]
0x00007fffffffd958│+0x0028: 0x0000000055575a8e
0x00007fffffffd960│+0x0030: 0x0000000000000004
0x00007fffffffd968│+0x0038: 0x0000555555678b00 → 0x0000000000000002
───────────────────────────────────────────────────────── code:x86:64 ────
0x555555634d1e <sstrncpy+151> mov rdx, rbx
0x555555634d21 <sstrncpy+154> lea rbx, [rdx+0x1]
0x555555634d25 <sstrncpy+158> movzx eax, BYTE PTR [rax]
→ 0x555555634d28 <sstrncpy+161> mov BYTE PTR [rdx], al
0x555555634d2a <sstrncpy+163> add DWORD PTR [rbp-0x14], 0x1
0x555555634d2e <sstrncpy+167> sub QWORD PTR [rbp-0x38], 0x1
0x555555634d33 <sstrncpy+172> mov rax, QWORD PTR [rbp-0x30]
0x555555634d37 <sstrncpy+176> movzx eax, BYTE PTR [rax]
0x555555634d3a <sstrncpy+179> test al, al
──────────────────────────────────────────────── source:sstrncpy.c+72 ────
67 }
68
69 d = dst;