[PATCH net-next v3 5/5] selinux: bpf: Add addtional check for bpf object file receive
Chenbo Feng
fengc at google.com
Thu Oct 12 18:28:13 UTC 2017
On Thu, Oct 12, 2017 at 5:25 AM, Stephen Smalley <sds at tycho.nsa.gov> wrote:
> On Wed, 2017-10-11 at 13:43 -0700, Chenbo Feng via Selinux wrote:
>> On Wed, Oct 11, 2017 at 5:54 AM, Stephen Smalley <sds at tycho.nsa.gov>
>> wrote:
>> > On Tue, 2017-10-10 at 17:09 -0700, Chenbo Feng wrote:
>> > > From: Chenbo Feng <fengc at google.com>
>> > >
>> > > Introduce a bpf object related check when sending and receiving
>> > > files
>> > > through unix domain socket as well as binder. It checks if the
>> > > receiving
>> > > process have privilege to read/write the bpf map or use the bpf
>> > > program.
>> > > This check is necessary because the bpf maps and programs are
>> > > using a
>> > > anonymous inode as their shared inode so the normal way of
>> > > checking
>> > > the
>> > > files and sockets when passing between processes cannot work
>> > > properly
>> > > on
>> > > eBPF object. This check only works when the BPF_SYSCALL is
>> > > configured.
>> > > The information stored inside the file security struct is the
>> > > same as
>> > > the information in bpf object security struct.
>> > >
>> > > Signed-off-by: Chenbo Feng <fengc at google.com>
>> > > ---
>> > > include/linux/lsm_hooks.h | 17 ++++++++++
>> > > include/linux/security.h | 9 ++++++
>> > > kernel/bpf/syscall.c | 27 ++++++++++++++--
>> > > security/security.c | 8 +++++
>> > > security/selinux/hooks.c | 67
>> > > +++++++++++++++++++++++++++++++++++++++
>> > > security/selinux/include/objsec.h | 9 ++++++
>> > > 6 files changed, 135 insertions(+), 2 deletions(-)
>> > >
>> > > diff --git a/include/linux/lsm_hooks.h
>> > > b/include/linux/lsm_hooks.h
>> > > index 7161d8e7ee79..517dea60b87b 100644
>> > > --- a/include/linux/lsm_hooks.h
>> > > +++ b/include/linux/lsm_hooks.h
>> > > @@ -1385,6 +1385,19 @@
>> > > * @bpf_prog_free_security:
>> > > * Clean up the security information stored inside bpf prog.
>> > > *
>> > > + * @bpf_map_file:
>> > > + * When creating a bpf map fd, set up the file security
>> > > information with
>> > > + * the bpf security information stored in the map struct. So
>> > > when the map
>> > > + * fd is passed between processes, the security module can
>> > > directly read
>> > > + * the security information from file security struct rather
>> > > than the bpf
>> > > + * security struct.
>> > > + *
>> > > + * @bpf_prog_file:
>> > > + * When creating a bpf prog fd, set up the file security
>> > > information with
>> > > + * the bpf security information stored in the prog struct. So
>> > > when the prog
>> > > + * fd is passed between processes, the security module can
>> > > directly read
>> > > + * the security information from file security struct rather
>> > > than the bpf
>> > > + * security struct.
>> > > */
>> > > union security_list_options {
>> > > int (*binder_set_context_mgr)(struct task_struct *mgr);
>> > > @@ -1726,6 +1739,8 @@ union security_list_options {
>> > > void (*bpf_map_free_security)(struct bpf_map *map);
>> > > int (*bpf_prog_alloc_security)(struct bpf_prog_aux *aux);
>> > > void (*bpf_prog_free_security)(struct bpf_prog_aux *aux);
>> > > + void (*bpf_map_file)(struct bpf_map *map, struct file
>> > > *file);
>> > > + void (*bpf_prog_file)(struct bpf_prog_aux *aux, struct file
>> > > *file);
>> > > #endif /* CONFIG_BPF_SYSCALL */
>> > > };
>> > >
>> > > @@ -1954,6 +1969,8 @@ struct security_hook_heads {
>> > > struct list_head bpf_map_free_security;
>> > > struct list_head bpf_prog_alloc_security;
>> > > struct list_head bpf_prog_free_security;
>> > > + struct list_head bpf_map_file;
>> > > + struct list_head bpf_prog_file;
>> > > #endif /* CONFIG_BPF_SYSCALL */
>> > > } __randomize_layout;
>> > >
>> > > diff --git a/include/linux/security.h b/include/linux/security.h
>> > > index 18800b0911e5..57573b794e2d 100644
>> > > --- a/include/linux/security.h
>> > > +++ b/include/linux/security.h
>> > > @@ -1740,6 +1740,8 @@ extern int security_bpf_map_alloc(struct
>> > > bpf_map *map);
>> > > extern void security_bpf_map_free(struct bpf_map *map);
>> > > extern int security_bpf_prog_alloc(struct bpf_prog_aux *aux);
>> > > extern void security_bpf_prog_free(struct bpf_prog_aux *aux);
>> > > +extern void security_bpf_map_file(struct bpf_map *map, struct
>> > > file
>> > > *file);
>> > > +extern void security_bpf_prog_file(struct bpf_prog_aux *aux,
>> > > struct
>> > > file *file);
>> > > #else
>> > > static inline int security_bpf(int cmd, union bpf_attr *attr,
>> > > unsigned int size)
>> > > @@ -1772,6 +1774,13 @@ static inline int
>> > > security_bpf_prog_alloc(struct bpf_prog_aux *aux)
>> > >
>> > > static inline void security_bpf_prog_free(struct bpf_prog_aux
>> > > *aux)
>> > > { }
>> > > +
>> > > +static inline void security_bpf_map_file(struct bpf_map *map,
>> > > struct
>> > > file *file)
>> > > +{ }
>> > > +
>> > > +static inline void security_bpf_prog_file(struct bpf_prog_aux
>> > > *aux,
>> > > + struct file *file)
>> > > +{ }
>> > > #endif /* CONFIG_SECURITY */
>> > > #endif /* CONFIG_BPF_SYSCALL */
>> > >
>> > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> > > index 1cf31ddd7616..aee69e564c50 100644
>> > > --- a/kernel/bpf/syscall.c
>> > > +++ b/kernel/bpf/syscall.c
>> > > @@ -324,11 +324,22 @@ static const struct file_operations
>> > > bpf_map_fops = {
>> > >
>> > > int bpf_map_new_fd(struct bpf_map *map, int flags)
>> > > {
>> > > + int fd;
>> > > + struct fd f;
>> > > if (security_bpf_map(map, OPEN_FMODE(flags)))
>> > > return -EPERM;
>> > >
>> > > - return anon_inode_getfd("bpf-map", &bpf_map_fops, map,
>> > > + fd = anon_inode_getfd("bpf-map", &bpf_map_fops, map,
>> > > flags | O_CLOEXEC);
>> > > + if (fd < 0)
>> > > + return fd;
>> > > +
>> > > + f = fdget(fd);
>> > > + if (!f.file)
>> > > + return -EBADF;
>> >
>> > This seems convoluted and unnecessarily inefficient, since
>> > anon_inode_getfd() has the struct file and could have directly
>> > returned
>> > it instead of having to go through fdget() on a fd we just
>> > installed.
>> > Also, couldn't the fd->file mapping have changed underneath us
>> > between
>> > fd_install() and fdget()?
>> > I would think it would be safer and more efficient to create an
>> > anon_inode_getfdandfile() or similar interface and use that, so
>> > that we
>> > can just pass the file it set up to the hook. Obviously that would
>> > need to be reviewed by the vfs folks.
>> >
>>
>> Do you mean create a anonymous inode interface specifically for eBPF
>> object? Is it okay that we add the hooks inside anon_inode_getfd and
>> pass the file to the hook before fd install.
>
> No, I meant to create a general helper, anon_inode_getfile(), that
> returns the file and the fd to the caller, and then the BPF-specific
> logic can stay in the BPF code.
>
> However, if storing the bpf type in the file_security_struct is in fact
> having a significant impact on per-file memory usage, then perhaps your
> original approach of exporting and testing the fops was the right one,
> albeit ugly.
>
It seems to me adding a bpf_type field inside the file_security_struct
have the same impact on selinux_file_security cache size as adding
both bpf_type and bpf_sid. Both implementation will cause a
significant increase on memory size. I am testing on a ARM 64bit
device and it might be different on x86 devices. I will return to the
original way to implement the bpf_ops check instead of adding new
field.
>> > > + security_bpf_map_file(map, f.file);
>> > > + fdput(f);
>> > > + return fd;
>> > > }
>> > >
>> > > int bpf_get_file_flag(int flags)
>> > > @@ -975,11 +986,23 @@ static const struct file_operations
>> > > bpf_prog_fops = {
>> > >
>> > > int bpf_prog_new_fd(struct bpf_prog *prog)
>> > > {
>> > > + int fd;
>> > > + struct fd f;
>> > > +
>> > > if (security_bpf_prog(prog))
>> > > return -EPERM;
>> > >
>> > > - return anon_inode_getfd("bpf-prog", &bpf_prog_fops, prog,
>> > > + fd = anon_inode_getfd("bpf-prog", &bpf_prog_fops, prog,
>> > > O_RDWR | O_CLOEXEC);
>> > > + if (fd < 0)
>> > > + return fd;
>> > > +
>> > > + f = fdget(fd);
>> > > + if (!f.file)
>> > > + return -EBADF;
>> > > + security_bpf_prog_file(prog->aux, f.file);
>> > > + fdput(f);
>> > > + return fd;
>> > > }
>> > >
>> > > static struct bpf_prog *____bpf_prog_get(struct fd f)
>> > > diff --git a/security/security.c b/security/security.c
>> > > index 1cd8526cb0b7..dacf649b8cfa 100644
>> > > --- a/security/security.c
>> > > +++ b/security/security.c
>> > > @@ -1734,4 +1734,12 @@ void security_bpf_prog_free(struct
>> > > bpf_prog_aux *aux)
>> > > {
>> > > call_void_hook(bpf_prog_free_security, aux);
>> > > }
>> > > +void security_bpf_map_file(struct bpf_map *map, struct file
>> > > *file)
>> > > +{
>> > > + call_void_hook(bpf_map_file, map, file);
>> > > +}
>> > > +void security_bpf_prog_file(struct bpf_prog_aux *aux, struct
>> > > file
>> > > *file)
>> > > +{
>> > > + call_void_hook(bpf_prog_file, aux, file);
>> > > +}
>> > > #endif /* CONFIG_BPF_SYSCALL */
>> > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> > > index 94e473b9c884..0a6ef20513b0 100644
>> > > --- a/security/selinux/hooks.c
>> > > +++ b/security/selinux/hooks.c
>> > > @@ -1815,6 +1815,10 @@ static inline int file_path_has_perm(const
>> > > struct cred *cred,
>> > > return inode_has_perm(cred, file_inode(file), av, &ad);
>> > > }
>> > >
>> > > +#ifdef CONFIG_BPF_SYSCALL
>> > > +static int bpf_file_check(struct file *file, u32 sid);
>> > > +#endif
>> > > +
>> > > /* Check whether a task can use an open file descriptor to
>> > > access an inode in a given way. Check access to the
>> > > descriptor itself, and then use dentry_has_perm to
>> > > @@ -1845,6 +1849,14 @@ static int file_has_perm(const struct cred
>> > > *cred,
>> > > goto out;
>> > > }
>> > >
>> > > +#ifdef CONFIG_BPF_SYSCALL
>> > > + if (fsec->bpf_type) {
>> > > + rc = bpf_file_check(file, cred_sid(cred));
>> > > + if (rc)
>> > > + goto out;
>> > > + }
>> > > +#endif
>> > > +
>> > > /* av is zero if only checking access to the descriptor. */
>> > > rc = 0;
>> > > if (av)
>> > > @@ -2165,6 +2177,14 @@ static int
>> > > selinux_binder_transfer_file(struct
>> > > task_struct *from,
>> > > return rc;
>> > > }
>> > >
>> > > +#ifdef CONFIG_BPF_SYSCALL
>> > > + if (fsec->bpf_type) {
>> > > + rc = bpf_file_check(file, sid);
>> > > + if (rc)
>> > > + return rc;
>> > > + }
>> > > +#endif
>> > > +
>> > > if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
>> > > return 0;
>> > >
>> > > @@ -6288,6 +6308,33 @@ static u32 bpf_map_fmode_to_av(fmode_t
>> > > fmode)
>> > > return av;
>> > > }
>> > >
>> > > +/* This function will check the file pass through unix socket or
>> > > binder to see
>> > > + * if it is a bpf related object. And apply correspinding checks
>> > > on
>> > > the bpf
>> > > + * object based on the type. The bpf maps and programs, not like
>> > > other files and
>> > > + * socket, are using a shared anonymous inode inside the kernel
>> > > as
>> > > their inode.
>> > > + * So checking that inode cannot identify if the process have
>> > > privilege to
>> > > + * access the bpf object and that's why we have to add this
>> > > additional check in
>> > > + * selinux_file_receive and selinux_binder_transfer_files.
>> > > + */
>> > > +static int bpf_file_check(struct file *file, u32 sid)
>> > > +{
>> > > + struct file_security_struct *fsec = file->f_security;
>> > > + int ret;
>> > > +
>> > > + if (fsec->bpf_type == BPF_MAP) {
>> > > + ret = avc_has_perm(sid, fsec->bpf_sid,
>> > > SECCLASS_BPF,
>> > > + bpf_map_fmode_to_av(file-
>> > > > f_mode), NULL);
>> > >
>> > > + if (ret)
>> > > + return ret;
>> > > + } else if (fsec->bpf_type == BPF_PROG) {
>> > > + ret = avc_has_perm(sid, fsec->bpf_sid,
>> > > SECCLASS_BPF,
>> > > + BPF__PROG_USE, NULL);
>> > > + if (ret)
>> > > + return ret;
>> > > + }
>> > > + return 0;
>> > > +}
>> > > +
>> > > static int selinux_bpf_map(struct bpf_map *map, fmode_t fmode)
>> > > {
>> > > u32 sid = current_sid();
>> > > @@ -6351,6 +6398,24 @@ static void selinux_bpf_prog_free(struct
>> > > bpf_prog_aux *aux)
>> > > aux->security = NULL;
>> > > kfree(bpfsec);
>> > > }
>> > > +
>> > > +static void selinux_bpf_map_file(struct bpf_map *map, struct
>> > > file
>> > > *file)
>> > > +{
>> > > + struct bpf_security_struct *bpfsec = map->security;
>> > > + struct file_security_struct *fsec = file->f_security;
>> > > +
>> > > + fsec->bpf_type = BPF_MAP;
>> > > + fsec->bpf_sid = bpfsec->sid;
>> > > +}
>> > > +
>> > > +static void selinux_bpf_prog_file(struct bpf_prog_aux *aux,
>> > > struct
>> > > file *file)
>> > > +{
>> > > + struct bpf_security_struct *bpfsec = aux->security;
>> > > + struct file_security_struct *fsec = file->f_security;
>> > > +
>> > > + fsec->bpf_type = BPF_PROG;
>> > > + fsec->bpf_sid = bpfsec->sid;
>> > > +}
>> > > #endif
>> > >
>> > > static struct security_hook_list selinux_hooks[]
>> > > __lsm_ro_after_init
>> > > = {
>> > > @@ -6581,6 +6646,8 @@ static struct security_hook_list
>> > > selinux_hooks[] __lsm_ro_after_init = {
>> > > LSM_HOOK_INIT(bpf_prog_alloc_security,
>> > > selinux_bpf_prog_alloc),
>> > > LSM_HOOK_INIT(bpf_map_free_security, selinux_bpf_map_free),
>> > > LSM_HOOK_INIT(bpf_prog_free_security,
>> > > selinux_bpf_prog_free),
>> > > + LSM_HOOK_INIT(bpf_map_file, selinux_bpf_map_file),
>> > > + LSM_HOOK_INIT(bpf_prog_file, selinux_bpf_prog_file),
>> > > #endif
>> > > };
>> > >
>> > > diff --git a/security/selinux/include/objsec.h
>> > > b/security/selinux/include/objsec.h
>> > > index 3d54468ce334..0162648761f9 100644
>> > > --- a/security/selinux/include/objsec.h
>> > > +++ b/security/selinux/include/objsec.h
>> > > @@ -67,11 +67,20 @@ struct inode_security_struct {
>> > > spinlock_t lock;
>> > > };
>> > >
>> > > +enum bpf_obj_type {
>> > > + BPF_MAP = 1,
>> > > + BPF_PROG,
>> > > +};
>> > > +
>> > > struct file_security_struct {
>> > > u32 sid; /* SID of open file description */
>> > > u32 fown_sid; /* SID of file owner (for
>> > > SIGIO) */
>> > > u32 isid; /* SID of inode at the time of file
>> > > open */
>> > > u32 pseqno; /* Policy seqno at the time of
>> > > file open */
>> > > +#ifdef CONFIG_BPF_SYSCALL
>> > > + unsigned char bpf_type;
>> > > + u32 bpf_sid;
>> > > +#endif
>> > > };
>> >
>> > Can you check how this impacts the size of the file_security_cache
>> > objects, and thus the memory overhead imposed on all open files?
>> >
>> > If it is significant, do we need to cache the bpf_sid here or could
>> > we
>> > just store the bpf_type and then dereference the bpfsec if it is a
>> > map
>> > or prog?
>> >
>> > From proc/slabinfo I find the number of object and the object size
>>
>> grows a lot after adding this two field. I will try to dereference
>> the
>> bpfsec instead to see if it helps.
>> > >
>> > > struct superblock_security_struct {
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