Re: [RFC PATCH v2 5/9] fs: add anon_inode_getfile_secure() similar to anon_inode_getfd_secure()

On Thu, Aug 12, 2021 at 5:32 AM Mickaël Salaün <mic(a)digikod.net&gt; wrote: > On 11/08/2021 22:48, Paul Moore wrote: >> Extending the secure anonymous inode support to other subsystems >> requires that we have a secure anon_inode_getfile() variant in >> addition to the existing secure anon_inode_getfd() variant. >> >> Thankfully we can reuse the existing __anon_inode_getfile() function >> and just wrap it with the proper arguments. >> >> Signed-off-by: Paul Moore <paul(a)paul-moore.com&gt; >> >> --- >> v2: >> - no change >> v1: >> - initial draft >> --- >> fs/anon_inodes.c | 29 +++++++++++++++++++++++++++++ >> include/linux/anon_inodes.h | 4 ++++ >> 2 files changed, 33 insertions(+) >> >> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c >> index a280156138ed..e0c3e33c4177 100644 >> --- a/fs/anon_inodes.c >> +++ b/fs/anon_inodes.c >> @@ -148,6 +148,35 @@ struct file *anon_inode_getfile(const char *name, >> } >> EXPORT_SYMBOL_GPL(anon_inode_getfile); >> >> +/** >> + * anon_inode_getfile_secure - Like anon_inode_getfile(), but creates a new >> + * !S_PRIVATE anon inode rather than reuse the >> + * singleton anon inode and calls the >> + * inode_init_security_anon() LSM hook. This >> + * allows for both the inode to have its own >> + * security context and for the LSM to enforce >> + * policy on the inode's creation. >> + * >> + * @name: [in] name of the "class" of the new file >> + * @fops: [in] file operations for the new file >> + * @priv: [in] private data for the new file (will be file's private_data) >> + * @flags: [in] flags >> + * @context_inode: >> + * [in] the logical relationship with the new inode (optional) >> + * >> + * The LSM may use @context_inode in inode_init_security_anon(), but a >> + * reference to it is not held. Returns the newly created file* or an error >> + * pointer. See the anon_inode_getfile() documentation for more information. >> + */ >> +struct file *anon_inode_getfile_secure(const char *name, >> + const struct file_operations *fops, >> + void *priv, int flags, >> + const struct inode *context_inode) >> +{ >> + return __anon_inode_getfile(name, fops, priv, flags, >> + context_inode, true); > > This is not directly related to this patch but why using the "secure" > boolean in __anon_inode_getfile() and __anon_inode_getfd() instead of > checking that context_inode is not NULL? This would simplify the code, > remove this anon_inode_getfile_secure() wrapper and avoid potential > inconsistencies. The issue is that it is acceptable for the context_inode to be either valid or NULL for callers who request the "secure" code path. Look at the SELinux implementation of the anonymous inode hook in selinux_inode_init_security_anon() and you will see that in cases where the context_inode is valid we simply inherit the label from the given inode, whereas if context_inode is NULL we do a type transition using the requesting task and the anonymous inode's "name".