On Wed, Aug 28, 2019 at 11:22:37AM +0200, Greg Kroah-Hartman wrote:
> On Tue, Aug 27, 2019 at 01:41:49PM -0700, Hridya Valsaraju wrote:
> > Currently, all binder state and statistics live in debugfs.
> > We need this information even when debugfs is not mounted.
> > This patch adds the mount option 'stats' to enable a binderfs
> > instance to have binder debug information present in the same.
> > 'stats=global' will enable the global binder statistics. In
> > the future, 'stats=local' will enable binder statistics local
> > to the binderfs instance. The two modes 'global' and 'local'
> > will be mutually exclusive. 'stats=global' option is only available
> > for a binderfs instance mounted in the initial user namespace.
> > An attempt to use the option to mount a binderfs instance in
> > another user namespace will return an EPERM error.
> >
> > Signed-off-by: Hridya Valsaraju <hridya@xxxxxxxxxx>
> > ---
> > drivers/android/binderfs.c | 47 ++++++++++++++++++++++++++++++++++++--
> > 1 file changed, 45 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
> > index cc2e71576396..d95d179aec58 100644
> > --- a/drivers/android/binderfs.c
> > +++ b/drivers/android/binderfs.c
> > @@ -51,18 +51,27 @@ static DEFINE_IDA(binderfs_minors);
> > /**
> > * binderfs_mount_opts - mount options for binderfs
> > * @max: maximum number of allocatable binderfs binder devices
> > + * @stats_mode: enable binder stats in binderfs.
> > */
> > struct binderfs_mount_opts {
> > int max;
> > + int stats_mode;
> > };
> >
> > enum {
> > Opt_max,
> > + Opt_stats_mode,
> > Opt_err
> > };
> >
> > +enum binderfs_stats_mode {
> > + STATS_NONE,
> > + STATS_GLOBAL,
> > +};
> > +
> > static const match_table_t tokens = {
> > { Opt_max, "max=%d" },
> > + { Opt_stats_mode, "stats=%s" },
> > { Opt_err, NULL }
> > };
> >
> > @@ -290,8 +299,9 @@ static void binderfs_evict_inode(struct inode *inode)
> > static int binderfs_parse_mount_opts(char *data,
> > struct binderfs_mount_opts *opts)
> > {
> > - char *p;
> > + char *p, *stats;
> > opts->max = BINDERFS_MAX_MINOR;
> > + opts->stats_mode = STATS_NONE;
> >
> > while ((p = strsep(&data, ",")) != NULL) {
> > substring_t args[MAX_OPT_ARGS];
> > @@ -311,6 +321,24 @@ static int binderfs_parse_mount_opts(char *data,
> >
> > opts->max = max_devices;
> > break;
> > + case Opt_stats_mode:
> > + stats = match_strdup(&args[0]);
> > + if (!stats)
> > + return -ENOMEM;
> > +
> > + if (strcmp(stats, "global") != 0) {
> > + kfree(stats);
> > + return -EINVAL;
> > + }
> > +
> > + if (!capable(CAP_SYS_ADMIN)) {
> > + kfree(stats);
> > + return -EINVAL;
>
> Can a non-CAP_SYS_ADMIN task even call this function? Anyway, if it
It can. A task that has CAP_SYS_ADMIN in the userns the corresponding
binderfs mount has been created in can change the max=<nr> mount option.
Only stats=global currently requires capable(CAP_SYS_ADMIN) aka
CAP_SYS_ADMIN in the initial userns to prevent non-initial userns from
snooping at global statistics.
> can, put the check at the top of the case, and just return early before
> doing any extra work like checking values or allocating memory.
>
> > + }
> > +
> > + opts->stats_mode = STATS_GLOBAL;
> > + kfree(stats);
> > + break;
> > default:
> > pr_err("Invalid mount options\n");
> > return -EINVAL;
> > @@ -322,8 +350,21 @@ static int binderfs_parse_mount_opts(char *data,
> >
> > static int binderfs_remount(struct super_block *sb, int *flags, char *data)
> > {
> > + int prev_stats_mode, ret;
> > struct binderfs_info *info = sb->s_fs_info;
> > - return binderfs_parse_mount_opts(data, &info->mount_opts);
> > +
> > + prev_stats_mode = info->mount_opts.stats_mode;
> > + ret = binderfs_parse_mount_opts(data, &info->mount_opts);
> > + if (ret)
> > + return ret;
> > +
> > + if (prev_stats_mode != info->mount_opts.stats_mode) {
> > + pr_info("Binderfs stats mode cannot be changed during a remount\n");
>
> pr_err()?
>
> thanks,
>
> greg k-h
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