procfs: expose umask in /proc/<PID>/status (3e42979e) · Commits · 戴 / test

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>

Documentation/filesystems/proc.txt

+1 −0

Original line number	Diff line number	Diff line
		@@ -225,6 +225,7 @@ Table 1-2: Contents of the status files (as of 4.1)
		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

fs/proc/array.c

+19 −1

Original line number	Diff line number	Diff line
		@@ -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(struct task_struct tsk)
		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_file m, struct pid_namespace ns,
		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;

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