security_co..._sid_default(9)

📦 version 7.3.1, in nixpkgs unstable

💖 security_context_to_sid_default — the Kernel API Manual glow-up 💖

okay bestie, so we're deep in the kernel today and the page we're stanning is security_context_to_sid_default(9) from the Kernel API Manual. it's giving "SELinux internals but make it make sense" and honestly? iconic. let's get into it 🎀

✨ NAME ✨

security_context_to_sid_default — get a SID for a security context, and if that doesn't work out, fall back to a default you specify. lowkey the safety-net friend of the SID family 🫶

🌸 SYNOPSIS 🌸

int security_context_to_sid_default (const char *scontext , u32
       scontext_len , u32 *sid , u32 def_sid , gfp_t gfp_flags );

like, five args, one int return, no cap. keep reading for what each one does 💅

🦋 ARGUMENTS 🦋

  • scontext — the security context itself, as a string. the main character of this function fr.
  • scontext_len — how long that context is, in bytes. yes, bytes. don't @ me.
  • sid — the security identifier (SID) — this is where the SID goes 👑
  • def_sid — the default SID to assign if something goes wrong. the backup dancer of this whole operation.
  • gfp_flags — the allocator get-free-page (GFP) flags. allocator vibes only ✨

💜 DESCRIPTION 💜

so what does it actually do? it obtains a SID that's associated with the security context whose string representation is specified by scontext. simple enough, right? 😌

now for the spicy part: the default SID is passed to the MLS layer to be used to allow kernel labeling of the MLS field if the MLS field is not present — that's the whole "upgrading to MLS without full relabel" situation. iykyk 🧚

also, it implicitly forces adding of the context even if it cannot be mapped yet. like, it just goes for it. bold. we respect it 💅

returns -EINVAL if the context is invalid, -ENOMEM if there's not enough memory available, or 0 on success. that's the whole vibe check right there ⭐

🌈 SEE ALSO 🌈

the kernel file is ./security/selinux/ss/services.c — that's the source of truth, bestie. and here's the whole friend group, all of them (9):

ngl, if any of these confuse you, go read them too — the whole SELinux services squad is like that 💀

and that's the page, bestie!! 💖 huge shoutout to the source at ./security/selinux/ss, dated October 2026, for the security_co..._sid_default(9) page in the Kernel API Manual. slay, periodt, go read your manpages 🌸✨🦋

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