Re: [PATCH ghak90 V5 03/10] audit: read container ID of a process

On 2019-03-18 07:10, Neil Horman wrote: > On Fri, Mar 15, 2019 at 02:29:51PM -0400, Richard Guy Briggs wrote: > > Add support for reading the audit container identifier from the proc > > filesystem. > > > > This is a read from the proc entry of the form > > /proc/PID/audit_containerid where PID is the process ID of the task > > whose audit container identifier is sought. > > > > The read expects up to a u64 value (unset: 18446744073709551615). > > > > This read requires CAP_AUDIT_CONTROL. > > > > Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; > > Acked-by: Serge Hallyn <serge(a)hallyn.com&gt; > > --- > > fs/proc/base.c | 23 +++++++++++++++++++++-- > > 1 file changed, 21 insertions(+), 2 deletions(-) > > > > diff --git a/fs/proc/base.c b/fs/proc/base.c > > index 2505c46c8701..0b833cbdf5b6 100644 > > --- a/fs/proc/base.c > > +++ b/fs/proc/base.c > > @@ -1295,6 +1295,24 @@ static ssize_t proc_sessionid_read(struct file * file, char __user * buf, > > .llseek = generic_file_llseek, > > }; > > > > +static ssize_t proc_contid_read(struct file *file, char __user *buf, > > + size_t count, loff_t *ppos) > > +{ > > + struct inode *inode = file_inode(file); > > + struct task_struct *task = get_proc_task(inode); > > + ssize_t length; > > + char tmpbuf[TMPBUFLEN*2]; > > + > Sorry, didn't notice this previously, but.. > Why *2 here? Its not wrong per-se, but would it be better to just change > TMPBUFLEN to be 22 bytes unilaterally? Its only ever used on stack calls that > arent that deep, and then you won't have to think about adjusting this call site > if you ever change the value of TMPBUFLEN in the future. TMPBUFLEN is 11 to accomodate a decimal representation of a u32 with terminating NULL. Since the contid is a u64, it was least disruptive and made sense to me to just double it. I could define a TMPBUFLEN2 to be 21 if you prefer?

> I'm fine with doing this in another patch later, but it seems like a worthwhile > cleanup > > functionality looks good beyond that nit. > > > + if (!task) > > + return -ESRCH; > > + /* if we don't have caps, reject */ > > + if (!capable(CAP_AUDIT_CONTROL)) > > + return -EPERM; > > + length = scnprintf(tmpbuf, TMPBUFLEN*2, "%llu", audit_get_contid(task)); > > + put_task_struct(task); > > + return simple_read_from_buffer(buf, count, ppos, tmpbuf, length); > > +} > > + > > static ssize_t proc_contid_write(struct file *file, const char __user *buf, > > size_t count, loff_t *ppos) > > { > > @@ -1325,6 +1343,7 @@ static ssize_t proc_contid_write(struct file *file, const char __user *buf, > > } > > > > static const struct file_operations proc_contid_operations = { > > + .read = proc_contid_read, > > .write = proc_contid_write, > > .llseek = generic_file_llseek, > > }; > > @@ -3039,7 +3058,7 @@ static int proc_stack_depth(struct seq_file *m, struct pid_namespace *ns, > > #ifdef CONFIG_AUDIT > > REG("loginuid", S_IWUSR|S_IRUGO, proc_loginuid_operations), > > REG("sessionid", S_IRUGO, proc_sessionid_operations), > > - REG("audit_containerid", S_IWUSR, proc_contid_operations), > > + REG("audit_containerid", S_IWUSR|S_IRUSR, proc_contid_operations), > > #endif > > #ifdef CONFIG_FAULT_INJECTION > > REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations), > > @@ -3428,7 +3447,7 @@ static int proc_tid_comm_permission(struct inode *inode, int mask) > > #ifdef CONFIG_AUDIT > > REG("loginuid", S_IWUSR|S_IRUGO, proc_loginuid_operations), > > REG("sessionid", S_IRUGO, proc_sessionid_operations), > > - REG("audit_containerid", S_IWUSR, proc_contid_operations), > > + REG("audit_containerid", S_IWUSR|S_IRUSR, proc_contid_operations), > > #endif > > #ifdef CONFIG_FAULT_INJECTION > > REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations), > > -- > > 1.8.3.1 > > > > > Acked-by: Neil Horman <nhorman(a)tuxdriver.com&gt; > - RGB -- Richard Guy Briggs <rgb(a)redhat.com&gt; Sr. S/W Engineer, Kernel Security, Base Operating Systems Remote, Ottawa, Red Hat Canada IRC: rgb, SunRaycer Voice: +1.647.777.2635, Internal: (81) 32635