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>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 8e65446..adfc5b4 100644 (file)
--- 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;