From 3e42979e65dace1f9268dd5440e5ab096b8dee59 Mon Sep 17 00:00:00 2001 From: "Richard W.M. Jones" Date: Fri, 20 May 2016 17:00:05 -0700 Subject: [PATCH] procfs: expose umask in /proc//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//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 Acked-by: Konstantin Khlebnikov Acked-by: Jerome Marchand Acked-by: Kees Cook Cc: "Theodore Ts'o" Cc: Michal Hocko Cc: Pierre Carrier Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/filesystems/proc.txt | 1 + fs/proc/array.c | 20 +++++++++++++++++++- 2 files changed, 20 insertions(+), 1 deletion(-) diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 7f5607a089b4..e8d00759bfa5 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -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 diff --git a/fs/proc/array.c b/fs/proc/array.c index b6c00ce0e29e..88c7de12197b 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -83,6 +83,7 @@ #include #include #include +#include #include #include @@ -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; -- 2.20.1