ipcctl_obtain_check(9)

💅 ipcctl_obtain_check — the manual page, but make it make sense

okay so bestie, welcome to ipcctl_obtain_check(9) from the Kernel API Manual ✨ this one's a little kernel-side helper that goes and fetches an ipc object for you and does the vibe check (permissions, audit, the whole thing) before letting you near it 🎀

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✨ NAME ✨

ipcctl_obtain_check — retrieve an ipc object and check permissions 🫶 like, grab the thing, then make sure you're actually allowed to touch it, no cap.

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🌸 SYNOPSIS 🌸

struct kern_ipc_perm * ipcctl_obtain_check (struct ipc_namespace *ns ,
struct ipc_ids *ids , int id , int cmd , struct ipc64_perm *perm , int
extra_perm );

literally that's the whole signature, copy it exactly, don't be weird about it 💅

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🦋 ARGUMENTS 🦋

• ns — the ipc namespace 🌈 that's the world we're digging around in.
• ids — the table of ids where to look for the ipc 👑 this is the little index we're searching through.
• id — the id of the ipc to retrieve 🎀 the specific one you want, bestie.
• cmd — the cmd to check ⭐ which command we're validating against, iykyk.
• perm — the permission to set 🔥 the perms being handed over.
• extra_perm — one extra permission parameter used by msq 💖 yes it's just the one extra one, and yes it's msq's little thing.

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💜 DESCRIPTION 💜

So this function does some common audit and permissions check for some IPC_XXX cmd, and it gets called from semctl_down, shmctl_down and msgctl_down 🌸 like, those three are the ones sliding into its DMs.

Here's the rundown, bestie:

• it retrieves the ipc object with the given id in the given table 👀
• then it performs some audit and permission check, depending on the given cmd 🧚 the vibe check is literally cmd-dependent, periodt.
• and then it returns a pointer to the ipc object, or otherwise, the corresponding error 😭 so either you get your object or you get told no.

⚠️ important one: call holding both the rwsem and the rcu read lock 💀 not one, not the other — both. Don't show up unlocked, bestie, that's not the move.

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🌟 SEE ALSO 🌟

Kernel file ./ipc/util.c — and honestly the whole friend group shows up here 🫶:

ipc_init(9), ipc_init_ids(9), ipc_init_proc_interface(9), ipc_findkey(9), ipc_addid(9), ipcget_new(9), ipc_check_perms(9), ipcget_public(9), ipc_kht_remove(9), ipc_search_maxidx(9), ipc_rmid(9), ipc_set_key_private(9), ipcperms(9), kernel_to_ipc64_perm(9), ipc64_perm_to_ipc_perm(9), ipc_obtain_object_idr(9), ipc_obtain_object_check(9), ipcget(9), ipc_update_perm(9), ipc_parse_version(9), sysvipc_find_ipc(9)

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and that's the page, bestie 🎀 this one came out of ./ipc and it's dated October 2026, filed under ipcctl_obtain_check(9) — go forth and hold your locks 💅✨