Just a formal note from me here.
On Fri 22-04-16 13:54:36, Andrew Morton wrote:
> From: "Richard W.M. Jones" <rjones@xxxxxxxxxx>
> Subject: procfs: expose umask in /proc/<PID>/status
>
> It's not possible to read the process umask without also modifying it,
> which is what umask(2) does. A library cannot read umask safely,
> especially if the main program might be multithreaded.
>
> Add a new status line ("Umask") in /proc/<PID>/status. It contains
> the file mode creation mask (umask) in octal. It is only shown for
> tasks which have task->fs.
>
> This patch is adapted from one originally written by Pierre Carrier.
>
>
> The use case is that we have endless trouble with people setting weird
> umask() values (usually on the grounds of "security"), and then everything
> breaking. I'm on the hook to fix these. We'd like to add debugging to
> our program so we can dump out the umask in debug reports.
>
> Previous versions of the patch used a syscall so you could only read your
> own umask. That's all I need. However there was quite a lot of push-back
> from those, so this new version exports it in /proc.
>
> See:
>
lkmlo.org links tend to be rather unstable from my experience. Please
try to use lkml.kernel.org/[rg]/$msg_id as much as possible
> https://lkml.org/lkml/2016/4/13/704 [umask2]
http://lkml.kernel.org/r/1460574336-18930-1-git-send-email-rjones@xxxxxxxxxx
> https://lkml.org/lkml/2016/4/13/487 [getumask]
http://lkml.kernel.org/r/1460547786-16766-1-git-send-email-rjones@xxxxxxxxxx
> Signed-off-by: Richard W.M. Jones <rjones@xxxxxxxxxx>
> Acked-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
> Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: "Theodore Ts'o" <tytso@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Pierre Carrier <pierre@xxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> Documentation/filesystems/proc.txt | 1 +
> fs/proc/array.c | 20 +++++++++++++++++++-
> 2 files changed, 20 insertions(+), 1 deletion(-)
>
> diff -puN Documentation/filesystems/proc.txt~procfs-expose-umask-in-proc-pid-status Documentation/filesystems/proc.txt
> --- a/Documentation/filesystems/proc.txt~procfs-expose-umask-in-proc-pid-status
> +++ a/Documentation/filesystems/proc.txt
> @@ -225,6 +225,7 @@ Table 1-2: Contents of the status files
> TracerPid PID of process tracing this process (0 if not)
> Uid Real, effective, saved set, and file system UIDs
> Gid Real, effective, saved set, and file system GIDs
> + Umask file mode creation mask
> FDSize number of file descriptor slots currently allocated
> Groups supplementary group list
> NStgid descendant namespace thread group ID hierarchy
> diff -puN fs/proc/array.c~procfs-expose-umask-in-proc-pid-status fs/proc/array.c
> --- a/fs/proc/array.c~procfs-expose-umask-in-proc-pid-status
> +++ a/fs/proc/array.c
> @@ -83,6 +83,7 @@
> #include <linux/tracehook.h>
> #include <linux/string_helpers.h>
> #include <linux/user_namespace.h>
> +#include <linux/fs_struct.h>
>
> #include <asm/pgtable.h>
> #include <asm/processor.h>
> @@ -139,12 +140,25 @@ static inline const char *get_task_state
> return task_state_array[fls(state)];
> }
>
> +static inline int get_task_umask(struct task_struct *tsk)
> +{
> + struct fs_struct *fs;
> + int umask = -ENOENT;
> +
> + task_lock(tsk);
> + fs = tsk->fs;
> + if (fs)
> + umask = fs->umask;
> + task_unlock(tsk);
> + return umask;
> +}
> +
> static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
> struct pid *pid, struct task_struct *p)
> {
> struct user_namespace *user_ns = seq_user_ns(m);
> struct group_info *group_info;
> - int g;
> + int g, umask;
> struct task_struct *tracer;
> const struct cred *cred;
> pid_t ppid, tpid = 0, tgid, ngid;
> @@ -162,6 +176,10 @@ static inline void task_state(struct seq
> ngid = task_numa_group_id(p);
> cred = get_task_cred(p);
>
> + umask = get_task_umask(p);
> + if (umask >= 0)
> + seq_printf(m, "Umask:\t%#04o\n", umask);
> +
> task_lock(p);
> if (p->files)
> max_fds = files_fdtable(p->files)->max_fds;
> _
>
> Patches currently in -mm which might be from rjones@xxxxxxxxxx are
>
> procfs-expose-umask-in-proc-pid-status.patch
--
Michal Hocko
SUSE Labs
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