Fix up non-directory creation in SGID directories
sgid directories have special semantics, making newly created files in the directory belong to the group of the directory, and newly created subdirectories will also become sgid. This is historically used for group-shared directories. But group directories writable by non-group members should not imply that such non-group members can magically join the group, so make sure to clear the sgid bit on non-directories for non-members (but remember that sgid without group execute means "mandatory locking", just to confuse things even more). Reported-by: Jann Horn <jannh@google.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [haggertk: Backported to 3.4 - Use capable() instead of capable_wrt_inode_uidgid()] CVE-2018-13405 Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org> Change-Id: I89974ab06a8ad22496031dbfd2c5106b6e64a0b8
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@ -1739,8 +1739,14 @@ void inode_init_owner(struct inode *inode, const struct inode *dir,
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inode->i_uid = current_fsuid();
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if (dir && dir->i_mode & S_ISGID) {
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inode->i_gid = dir->i_gid;
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/* Directories are special, and always inherit S_ISGID */
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if (S_ISDIR(mode))
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mode |= S_ISGID;
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else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) &&
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!in_group_p(inode->i_gid) &&
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!capable(CAP_FSETID))
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mode &= ~S_ISGID;
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} else
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inode->i_gid = current_fsgid();
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inode->i_mode = mode;
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