proc: don't use FOLL_FORCE for reading cmdline and environment

Now that Lorenzo cleaned things up and made the FOLL_FORCE users
explicit, it becomes obvious how some of them don't really need
FOLL_FORCE at all.

So remove FOLL_FORCE from the proc code that reads the command line and
arguments from user space.

The mem_rw() function actually does want FOLL_FORCE, because gdd (and
possibly many other debuggers) use it as a much more convenient version
of PTRACE_PEEKDATA, but we should consider making the FOLL_FORCE part
conditional on actually being a ptracer.  This does not actually do
that, just moves adds a comment to that effect and moves the gup_flags
settings next to each other.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 10 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 8e654468ab67..adfc5b4986f5 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -252,7 +252,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
          * Inherently racy -- command line shares address space
          * with code and data.
          */
-        rv = access_remote_vm(mm, arg_end - 1, &c, 1, FOLL_FORCE);
+        rv = access_remote_vm(mm, arg_end - 1, &c, 1, 0);
         if (rv <= 0)
                 goto out_free_page;
 
@@ -270,8 +270,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
                         int nr_read;
 
                         _count = min3(count, len, PAGE_SIZE);
-                        nr_read = access_remote_vm(mm, p, page, _count,
-                                        FOLL_FORCE);
+                        nr_read = access_remote_vm(mm, p, page, _count, 0);
                         if (nr_read < 0)
                                 rv = nr_read;
                         if (nr_read <= 0)
@@ -306,8 +305,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
                         bool final;
 
                         _count = min3(count, len, PAGE_SIZE);
-                        nr_read = access_remote_vm(mm, p, page, _count,
-                                        FOLL_FORCE);
+                        nr_read = access_remote_vm(mm, p, page, _count, 0);
                         if (nr_read < 0)
                                 rv = nr_read;
                         if (nr_read <= 0)
@@ -356,8 +354,7 @@ skip_argv:
                         bool final;
 
                         _count = min3(count, len, PAGE_SIZE);
-                        nr_read = access_remote_vm(mm, p, page, _count,
-                                        FOLL_FORCE);
+                        nr_read = access_remote_vm(mm, p, page, _count, 0);
                         if (nr_read < 0)
                                 rv = nr_read;
                         if (nr_read <= 0)
@@ -835,7 +832,7 @@ static ssize_t mem_rw(struct file *file, char __user *buf,
         unsigned long addr = *ppos;
         ssize_t copied;
         char *page;
-        unsigned int flags = FOLL_FORCE;
+        unsigned int flags;
 
         if (!mm)
                 return 0;
@@ -848,6 +845,8 @@ static ssize_t mem_rw(struct file *file, char __user *buf,
         if (!atomic_inc_not_zero(&mm->mm_users))
                 goto free;
 
+        /* Maybe we should limit FOLL_FORCE to actual ptrace users? */
+        flags = FOLL_FORCE;
         if (write)
                 flags |= FOLL_WRITE;
 
@@ -971,8 +970,7 @@ static ssize_t environ_read(struct file *file, char __user *buf,
                 max_len = min_t(size_t, PAGE_SIZE, count);
                 this_len = min(max_len, this_len);
 
-                retval = access_remote_vm(mm, (env_start + src),
-                        page, this_len, FOLL_FORCE);
+                retval = access_remote_vm(mm, (env_start + src), page, this_len, 0);
 
                 if (retval <= 0) {
                         ret = retval;