secprog(3)

💅 secprog(3) — Secure Programming Library, but make it understandable

okay bestie, listen up — this is the secprog(3) page from the Secure Programming Library, and it's lowkey a whole buffet of secure replacements for the sketchy libc functions you'd otherwise use. it's giving "responsible adult energy" and honestly? we love that for us. 💖

---

✨ NAME ✨

so here's the cast of characters, all from secprog:

• s_strncpy — secure strncpy
• s_strncat — secure strncat
• s_execv — secure execv
• s_tmpfile — secure buffered tmp file
• s_popen — secure popen
• safe_tmpfile — secure unbuffered tmp file
• safe_reopen — secure reopen of files
• sigprotection — blocking signals
• close_stdfds — close standard file descriptors
• setlimits — set limits
• setupsbitproc — setup at beginning of setuid code

---

🎀 SYNOPSIS 🎀

like, grab the header first, obviously:

#include <secprog.h>

and then all the signatures, verbatim, because we do not play with prototypes:

char *s_strncpy(char *dest, char *src, size_t n);

char *s_strncat(char *dest, char *src, size_t n);

int s_execv(const char *filename, char *const argv[]);

FILE *s_tmpfile(void);

FILE *s_popen(char *cmd, const char *type);

int safe_tmpfile(char *filename);

int safe_reopen(char *file, int mode);

int sigprotection(u_int toggle, sigset_t *sp_blockmask);

int close_stdfds(void);

int setlimits(sl_limit slim);

int setupsbitproc(void);

---

🌸 DESCRIPTION 🌸

okay so let's go function by function, no skipping, periodt.

• s_strncpy — copys string src to buffer dest up to size n. the dest string is zero terminated. that's it, that's the vibe. 🫶
• s_strncat — concatenate string src with dest up to size n. the dest string is zero terminated. iconic behavior, honestly.
• s_execv — executes filename with arguments argv. and the way that it's thorough? it cleans up the environment, checks the login, checks the current directory, and sets the close_on_exec flag for all filedescriptors expect stdin, stdout, stderr. (yes, "expect" — that's what the page says, don't come for me 😭). it's giving main character security energy. 🔥
• s_tmpfile — creates a temp file more securely and returns a FILE *. cute and safe, we stan.
• s_popen — this is a secure popen(3) that avoids using the shell. no shell, no problems, lowkey brilliant. 💅
• safe_tempfile — works like s_tempfile expect that it returns an integer as filedescriptor. (again, "expect" — preserving the lore exactly as written, bestie. don't @ me.) 🙈
• safe_reopen — reopens a file securely even in world-writeable directories like /tmp. the way that it protects you in the wild west of /tmp? obsessed. 🦋
• sigprotection — should be called before and after a critical code part. the toggle variable should be SP_ON for activating the signals set in mask sp_blockmask or SP_OFF for switching signal blocking off. so basically: wrap your critical section like a little security blanket. 🧚
• close_stdfds — just closes all standard filedescriptors. (Note: Just needed on systems with old glibc, or old OpenBSD kernel.) so like, vintage systems only, iykyk. 💀
• setlimits — uses the structure slim to set process limites like: RLIMIT_MEMLOCK, RLIMIT_NPROC, RLIMIT_NOFILE, RLIMIT_RSS, RLIMIT_CORE, RLIMIT_STACK, RLIMIT_DATA, RLIMIT_FSIZE. and yes, "limites" — the page said it, I'm keeping it. here's the struct in all its glory:

typedef struct
{
  int fsize;          /* max file size */
  int data;           /* max data size */
  int stack;          /* max stack size */
  int core;           /* max core file size */
  int rss;            /* max resident set size */
  int nproc;          /* max number of processes */
  int nofile;         /* max number of open files */
  int memlock;        /* max locked-in-memory address space */
} sl_limit;

• setupsbitproc — should be called at the beginning of every setuid application to close the standard filedescriptors and to set some process limits. (Note: It does not drop setuid privileges.) so important, bestie — it's a setup step, not a full privilege drop. don't get it twisted. ⚠️

---

🦋 RETURN VALUE 🦋

okay so what do you get back? let's break it down:

• the function s_strncat and s_strncpy return a pointer to the resulting string.. (yes, two dots — we're keeping the punctuation energy. periodt.)
• the function s_popen returns a buffered filedescriptor on success, NULL otherwise.
• the function s_execv does not return on success, returns -1 otherwise.
• the function s_tmpfile returns a buffered filedescriptor on success, NULL otherwise.
• the function safe_tmpfile returns a filedescriptor on success, -1 otherwise.
• the function safe_reopen returns a filedescriptor on success, -1 otherwise.
• the function sigprotection returns zero on success, -1 otherwise.
• the function close_stdfds returns zero on success, -1 otherwise.
• the function setlimits returns zero on success, -1 otherwise.
• the function setupsbitproc returns zero on success, -1 otherwise.

---

🌈 SEE ALSO 🌈

go touch grass and read these too, bestie:

strncpy(3), strncat(3), popen(3), exec(3).

---

okay that's the whole page, and honestly? you ate that. 💅✨

this absolute icon of a manpage was brought to you by Thomas Biege <thomas@suse.de>, dated 22 Apr 2004 — a whole legend, no cap. 🫶👑