mode_strip_sgid(9)

💅 mode_strip_sgid — Kernel API Manual 🎀

okay so bestie, welcome to mode_strip_sgid(9), the little kernel function that does the sgid bit vibe check for non-directories ✨

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🌸 NAME 🌸

mode_strip_sgid — handles the sgid bit for non-directories, no cap 💅

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✨ SYNOPSIS ✨

umode_t mode_strip_sgid (struct mnt_idmap *idmap , const struct inode
*dir , umode_t mode );

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🦋 ARGUMENTS 🦋

• idmap — the idmap of the mount that the inode was created from 🗺️
• dir — the parent directory inode (the one it's all happening in) 📁
• mode — the mode of the file that's gonna be created in dir 🎀

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💖 DESCRIPTION 💖

okay so here's the situation, and honestly it's giving permission-check main character energy 👑

If the mode of the new file has both the S_ISGID and S_IXGRP bit raised, and dir has the S_ISGID bit raised too — then this function makes sure the caller is either in the group of the parent directory, or they have CAP_FSETID in their user namespace and are privileged over the parent directory. iykyk, that's the whole security vibe check 🛡️

In all other cases, it strips the S_ISGID bit from mode. literally just takes it right off, bye 👋

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⭐ RETURN ⭐

the new mode to use for the file — that's it, that's the return value 💫

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🌈 SEE ALSO 🌈

all the kernel file friends from ./fs/inode.c, because we support each other's slay 🫶

• inode_init_always_gfp(9)
• alloc_inode(9)
• drop_nlink(9)
• clear_nlink(9)
• set_nlink(9)
• inc_nlink(9)
• inode_sb_list_add(9)
• __insert_inode_hash(9)
• __remove_inode_hash(9)
• evict_inodes(9)
• new_inode(9)
• unlock_new_inode(9)
• lock_two_nondirectories(9)
• unlock_two_nondirectories(9)
• inode_insert5(9)
• iget5_locked(9)
• iget5_locked_rcu(9)
• iget_locked(9)
• iunique(9)
• ihold(9)
• ilookup5_nowait(9)
• ilookup5(9)
• ilookup(9)
• find_inode_nowait(9)
• find_inode_rcu(9)
• find_inode_by_ino_rcu(9)
• iput(9)
• iput_not_last(9)
• bmap(9)
• inode_update_time(9)
• generic_update_time(9)
• atime_needs_update(9)
• file_remove_privs(9)
• current_time(9)
• file_update_time(9)
• file_modified_flags(9)
• file_modified(9)
• kiocb_modified(9)
• inode_init_owner(9)
• inode_owner_or_capable(9)
• inode_dio_wait(9)
• timestamp_truncate(9)
• inode_set_ctime_current(9)
• inode_set_ctime_deleg(9)
• in_group_or_capable(9)
• dump_inode(9)

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🧚 friendly reminder bestie: if that sgid check doesn't pass, the bit is gone, and there is no "undo" button 🫶

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💜 that's the page!! this one lives in ./fs, from the Kernel API Manual, dated October 2026 — mode_strip_sgid(9), periodt 🎀✨🌸