On 2020-03-02, David Howells <dhowells@xxxxxxxxxx> wrote: > Christian Brauner <christian.brauner@xxxxxxxxxx> wrote: > > > I think we settled this and can agree on RESOLVE_NO_SYMLINKS being the > > right thing to do, i.e. not resolving symlinks will stay opt-in. > > Or is your worry even with the current semantics of openat2()? I don't > > see the issue since O_NOFOLLOW still works with openat2(). > > Say, for example, my home dir is on a network volume somewhere and /home has a > symlink pointing to it. RESOLVE_NO_SYMLINKS cannot be used to access a file > inside my homedir if the pathwalk would go through /home/dhowells - this would > affect fsinfo() Yes, though this only happens if you're opening "/home/dhowells/foobar". If you are doing "./foobar" from within "/home/dhowells" it will work (or if you open a dirfd to "/home/dhowells") -- because no symlink resolution is done as part of that openat2() call. > So RESOLVE_NO_SYMLINKS is not a substitute for AT_SYMLINK_NOFOLLOW > (O_NOFOLLOW would not come into it). This is what I was saying up-thread -- the semantics are not the same *on purpose*. If you want "don't follow symlinks *only for the final component*" then you need to have an AT_SYMLINK_NOFOLLOW equivalent. My counter-argument is that most people actually want RESOLVE_NO_SYMLINKS (as evidenced by the countless symlink-related security bugs -- many of which used O_NOFOLLOW incorrectly), it just wasn't available before Linux 5.6. -- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH <https://www.cyphar.com/>
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