memdup_user_nul(9)

💖 memdup_user_nul(9) 💖

ok so bestie, you found it — the page for memdup_user_nul, straight out of the Kernel API Manual (section 9, kernel-space edition, we're fancy today 🎀). This one's a little baby function that copies some bytes out of user space and makes sure the result is NUL-terminated. Ngl it's short, but it eats.

---

✨ NAME ✨

memdup_user_nul — duplicate a memory region from user space and NUL-terminate it 🫶

---

🌸 SYNOPSIS 🌸

void * memdup_user_nul (const void __user *src , size_t len );

---

🦋 ARGUMENTS 🦋

• src — the source address, and it lives in user space (yes, the __user is doing the heavy lifting here 👀).
• len — how many bytes we're copying, periodt.

---

⭐ RETURN ⭐

On failure you get an ERR_PTR back. That's the whole vibe the page gives us — it's literally the only thing documented under RETURN 😭 so like, check the return value properly, IS_ERR() girlies know what's up. (The success return is not spelled out here, so I'm not gonna make it up for you 💅.)

---

🔥 SEE ALSO 🔥

• Kernel file ./mm/util.c
• kfree_const(9)
• __kmemdup_nul(9)
• kstrdup(9)
• kstrdup_const(9)
• kstrndup(9)
• kmemdup(9)
• kmemdup_array(9)
• kvmemdup(9)
• kmemdup_nul(9)
• memdup_user(9)
• vmemdup_user(9)
• strndup_user(9)
• randomize_page(9)
• __account_locked_vm(9)
• account_locked_vm(9)
• __vmalloc_array(9)
• vmalloc_array(9)
• __vcalloc(9)
• vcalloc(9)
• folio_mapping(9)
• folio_copy(9)
• get_cmdline(9)
• mem_dump_obj(9)
• compat_set_desc_from_vma(9)
• __compat_vma_mmap(9)
• compat_vma_mmap(9)
• snapshot_page(9)
• mmap_action_prepare(9)
• mmap_action_complete(9)
• folio_pte_batch(9)
• page_range_contiguous(9)

lowkey that's a whole friend group of memory-copying functions and I love that for them 🌈

---

and that's the whole page, bestie — no cap, it's a short one 🍓

this iconic little writeup lives under ./mm in the Kernel API Manual, dated October 2026 — mwah, see u in the next man page 💜🧚‍♀️