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    SubjectRe: [PATCH 2/2] sysctl: Restore the selinux path based label lookup for sysctls.
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    On Wed, 2007-02-07 at 13:24 -0500, Stephen Smalley wrote:
    > On Tue, 2007-02-06 at 14:21 -0700, Eric W. Biederman wrote:
    > > This time instead of generating the generating the paths from proc_dir_entries
    > > generate the labels from the names in the sysctl ctl_tables themselves. This
    > > removes an unnecessary layer of indirection, allows this to work even when
    > > procfs support is not compiled into the kernel, and especially allows it
    > > to work now that ctl_tables no longer have a proc_dir_entry field.
    >
    > Thanks, looks sane.
    >
    > > I continue passing "proc" into genfs sid although that is complete nonsense
    > > to allow existing selinux policies to work without modification.
    > >
    > > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
    >
    > Acked-by: Stephen Smalley <sds@tycho.nsa.gov>

    Hmmm...but in testing the patch, I don't seem to (consistently) reach
    these checks when accessing via /proc/sys. I see that you are caching
    the mode information and using it in some cases rather than calling the
    sysctl_perm function.

    One related but separate issue is that the /proc/sys inode labeling is
    also affected by the sysctl patch series. Those inodes used to be
    labeled by selinux_proc_get_sid (from selinux_d_instantiate), but that
    no longer works, so they now fall back to the superblock SID (generic
    proc label). That changes the inode permission checks on an attempt to
    access a /proc/sys node and will likely cause denials under current
    policy for confined domains since one wouldn't generally be writing to
    the generic proc label. If you always called sysctl_perm from the proc
    sysctl code, we could possibly dispense with inode permission checking
    on those inodes, e.g. marking them private.

    >
    > > ---
    > > security/selinux/hooks.c | 43 +++++++++++++++++++++++++++++++++++++++++--
    > > 1 files changed, 41 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
    > > index 3a36057..c17a8dd 100644
    > > --- a/security/selinux/hooks.c
    > > +++ b/security/selinux/hooks.c
    > > @@ -1424,6 +1424,41 @@ static int selinux_capable(struct task_struct *tsk, int cap)
    > > return task_has_capability(tsk,cap);
    > > }
    > >
    > > +static int selinux_sysctl_get_sid(ctl_table *table, u16 tclass, u32 *sid)
    > > +{
    > > + int buflen, rc;
    > > + char *buffer, *path, *end;
    > > +
    > > + rc = -ENOMEM;
    > > + buffer = (char*)__get_free_page(GFP_KERNEL);
    > > + if (!buffer)
    > > + goto out;
    > > +
    > > + buflen = PAGE_SIZE;
    > > + end = buffer+buflen;
    > > + *--end = '\0';
    > > + buflen--;
    > > + path = end-1;
    > > + *path = '/';
    > > + while (table) {
    > > + const char *name = table->procname;
    > > + size_t namelen = strlen(name);
    > > + buflen -= namelen + 1;
    > > + if (buflen < 0)
    > > + goto out_free;
    > > + end -= namelen;
    > > + memcpy(end, name, namelen);
    > > + *--end = '/';
    > > + path = end;
    > > + table = table->parent;
    > > + }
    > > + rc = security_genfs_sid("proc", path, tclass, sid);
    > > +out_free:
    > > + free_page((unsigned long)buffer);
    > > +out:
    > > + return rc;
    > > +}
    > > +
    > > static int selinux_sysctl(ctl_table *table, int op)
    > > {
    > > int error = 0;
    > > @@ -1438,8 +1473,12 @@ static int selinux_sysctl(ctl_table *table, int op)
    > >
    > > tsec = current->security;
    > >
    > > - /* Use the well-defined sysctl SID. */
    > > - tsid = SECINITSID_SYSCTL;
    > > + rc = selinux_sysctl_get_sid(table, (op == 0001) ?
    > > + SECCLASS_DIR : SECCLASS_FILE, &tsid);
    > > + if (rc) {
    > > + /* Default to the well-defined sysctl SID. */
    > > + tsid = SECINITSID_SYSCTL;
    > > + }
    > >
    > > /* The op values are "defined" in sysctl.c, thereby creating
    > > * a bad coupling between this module and sysctl.c */
    --
    Stephen Smalley
    National Security Agency

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