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:
https://lkml.org/lkml/2016/4/13/704 [umask2]
https://lkml.org/lkml/2016/4/13/487 [getumask]
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Acked-by: Konstantin Khlebnikov <koct9i@gmail.com>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Pierre Carrier <pierre@spotify.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 7f5607a..e8d0075 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -225,6 +225,7 @@
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 --git a/fs/proc/array.c b/fs/proc/array.c
index b6c00ce..88c7de1 100644
--- a/fs/proc/array.c
+++ b/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 @@
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 @@
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;