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fanotify: disallow mount/sb marks on kernel internal pseudo fs
Hopefully, nobody is trying to abuse mount/sb marks for watching all
anonymous pipes/inodes.
I cannot think of a good reason to allow this - it looks like an
oversight that dated back to the original fanotify API.
Link: https://lore.kernel.org/linux-fsdevel/20230628101132.kvchg544mczxv2pm@quack3/
Fixes: 0ff21db9fc
("fanotify: hooks the fanotify_mark syscall to the vfsmount code")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230629042044.25723-1-amir73il@gmail.com>
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@ -1622,6 +1622,20 @@ static int fanotify_events_supported(struct fsnotify_group *group,
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path->mnt->mnt_sb->s_type->fs_flags & FS_DISALLOW_NOTIFY_PERM)
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return -EINVAL;
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/*
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* mount and sb marks are not allowed on kernel internal pseudo fs,
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* like pipe_mnt, because that would subscribe to events on all the
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* anonynous pipes in the system.
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*
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* SB_NOUSER covers all of the internal pseudo fs whose objects are not
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* exposed to user's mount namespace, but there are other SB_KERNMOUNT
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* fs, like nsfs, debugfs, for which the value of allowing sb and mount
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* mark is questionable. For now we leave them alone.
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*/
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if (mark_type != FAN_MARK_INODE &&
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path->mnt->mnt_sb->s_flags & SB_NOUSER)
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return -EINVAL;
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/*
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* We shouldn't have allowed setting dirent events and the directory
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* flags FAN_ONDIR and FAN_EVENT_ON_CHILD in mask of non-dir inode,
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