From: Al Viro <viro@zeniv.linux.org.uk>
To: KP Singh <kpsingh@kernel.org>
Cc: bpf@vger.kernel.org, linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
Yosry Ahmed <yosryahmed@google.com>
Subject: Re: [PATCH v5 bpf-next 4/5] bpf: Add a bpf_getxattr kfunc
Date: Tue, 28 Jun 2022 18:23:05 +0100 [thread overview]
Message-ID: <Yrs4+ThR4ACb5eD/@ZenIV> (raw)
In-Reply-To: <20220628161948.475097-5-kpsingh@kernel.org>
On Tue, Jun 28, 2022 at 04:19:47PM +0000, KP Singh wrote:
> LSMs like SELinux store security state in xattrs. bpf_getxattr enables
> BPF LSM to implement similar functionality. In combination with
> bpf_local_storage, xattrs can be used to develop more complex security
> policies.
>
> This kfunc wraps around __vfs_getxattr which can sleep and is,
> therefore, limited to sleepable programs using the newly added
> sleepable_set for kfuncs.
"Sleepable" is nowhere near enough - for a trivial example, consider
what e.g. ext2_xattr_get() does.
down_read(&EXT2_I(inode)->xattr_sem);
in there means that having that thing executed in anything that happens
to hold ->xattr_sem is a deadlock fodder.
"Can't use that in BPF program executed in non-blocking context" is
*not* sufficient to make it safe.
next prev parent reply other threads:[~2022-06-28 17:23 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-28 16:19 [PATCH v5 bpf-next 0/5] Add bpf_getxattr KP Singh
2022-06-28 16:19 ` [PATCH v5 bpf-next 1/5] btf: Add a new kfunc set which allows to mark a function to be sleepable KP Singh
2022-06-28 16:19 ` [PATCH v5 bpf-next 2/5] bpf: kfunc support for ARG_PTR_TO_CONST_STR KP Singh
2022-06-28 16:19 ` [PATCH v5 bpf-next 3/5] bpf: Allow kfuncs to be used in LSM programs KP Singh
2022-06-28 16:19 ` [PATCH v5 bpf-next 4/5] bpf: Add a bpf_getxattr kfunc KP Singh
2022-06-28 17:22 ` Christian Brauner
2022-06-28 17:23 ` Al Viro [this message]
2022-06-28 17:29 ` KP Singh
2022-06-28 16:19 ` [PATCH v5 bpf-next 5/5] bpf/selftests: Add a selftest for bpf_getxattr KP Singh
2022-06-28 17:33 ` Christian Brauner
2022-06-28 17:52 ` KP Singh
2022-06-28 22:28 ` Alexei Starovoitov
2022-06-29 8:11 ` Christian Brauner
2022-06-29 9:55 ` Christian Brauner
2022-06-30 3:02 ` Alexei Starovoitov
2022-06-30 11:45 ` Christian Brauner
2022-06-30 12:21 ` KP Singh
2022-06-30 12:23 ` KP Singh
2022-06-30 13:26 ` Christian Brauner
2022-06-30 13:29 ` KP Singh
2022-06-30 13:47 ` Christian Brauner
2022-06-30 14:37 ` Christian Brauner
2022-06-30 16:10 ` Casey Schaufler
2022-06-30 22:23 ` KP Singh
2022-06-30 23:23 ` Casey Schaufler
2022-07-01 8:32 ` Amir Goldstein
2022-07-01 8:58 ` Christian Brauner
2022-07-01 9:24 ` Amir Goldstein
2022-06-30 16:28 ` Amir Goldstein
2022-06-30 22:25 ` KP Singh
2022-06-28 17:13 ` [PATCH v5 bpf-next 0/5] Add bpf_getxattr Christian Brauner
2022-06-28 17:20 ` KP Singh
2022-06-28 17:21 ` KP Singh
2022-06-29 1:36 ` Dave Chinner
2022-06-29 2:00 ` KP Singh
2022-06-29 2:05 ` KP Singh
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