linux-kernel - Re: [PATCH bpf-next 1/2] fs/xattr: bpf: Introduce security.bpf xattr name prefix

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Message-ID: <8F600063-A87F-4613-A0DB-AC964E9C2903@fb.com>
Date: Mon, 7 Oct 2024 17:15:47 +0000
From: Song Liu <songliubraving@...a.com>
To: Jiri Olsa <olsajiri@...il.com>
CC: Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        Linux-Fsdevel
	<linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel
 Team <kernel-team@...a.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Eduard
 Zingerman <eddyz87@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel
 Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Al
 Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan
 Kara <jack@...e.cz>,
        KP Singh <kpsingh@...nel.org>,
        Matt Bobrowski
	<mattbobrowski@...gle.com>
Subject: Re: [PATCH bpf-next 1/2] fs/xattr: bpf: Introduce security.bpf xattr
 name prefix

Hi Jiri,

Thanks for the review!

> On Oct 7, 2024, at 1:39 AM, Jiri Olsa <olsajiri@...il.com> wrote:
> 
> On Wed, Oct 02, 2024 at 02:46:36PM -0700, Song Liu wrote:
>> Introduct new xattr name prefix security.bpf, and enable reading these
>> xattrs from bpf kfuncs bpf_get_[file|dentry]_xattr(). Note that
>> "security.bpf" could be the name of the xattr or the prefix of the
>> name. For example, both "security.bpf" and "security.bpf.xxx" are
>> valid xattr name; while "security.bpfxxx" is not valid.
>> 
>> Signed-off-by: Song Liu <song@...nel.org>
>> ---
>> fs/bpf_fs_kfuncs.c         | 19 ++++++++++++++++++-
>> include/uapi/linux/xattr.h |  4 ++++
>> 2 files changed, 22 insertions(+), 1 deletion(-)
>> 
>> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
>> index 3fe9f59ef867..339c4fef8f6e 100644
>> --- a/fs/bpf_fs_kfuncs.c
>> +++ b/fs/bpf_fs_kfuncs.c
>> @@ -93,6 +93,23 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
>> return len;
>> }
>> 
>> +static bool bpf_xattr_name_allowed(const char *name__str)
>> +{
>> + /* Allow xattr names with user. prefix */
>> + if (!strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
>> + return true;
>> +
>> + /* Allow security.bpf. prefix or just security.bpf */
>> + if (!strncmp(name__str, XATTR_NAME_BPF_LSM, XATTR_NAME_BPF_LSM_LEN) &&
>> +    (name__str[XATTR_NAME_BPF_LSM_LEN] == '\0' ||
>> +     name__str[XATTR_NAME_BPF_LSM_LEN] == '.')) {
>> + return true;
>> + }
>> +
>> + /* Disallow anything else */
>> + return false;
>> +}
>> +
>> /**
>>  * bpf_get_dentry_xattr - get xattr of a dentry
>>  * @dentry: dentry to get xattr from
>> @@ -117,7 +134,7 @@ __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__st
> 
> nit, I guess the comment for bpf_get_dentry_xattr function needs to be updated
> 
> * For security reasons, only *name__str* with prefix "user." is allowed.

Good catch! We can update it as:

 * For security reasons, only *name__str* with prefix "user." or
 * "security.bpf" is allowed.

Song