[PATCH 4.4 82/88] proc: dont use FOLL_FORCE for reading cmdline and environment

Greg Kroah-Hartman
2018-12-14T12:17:08Z

From: Linus Torvalds <torvalds@linux-foundation.org>

commit 272ddc8b37354c3fe111ab26d25e792629148eee upstream.

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>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/proc/base.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -254,7 +254,7 @@ static ssize_t proc_pid_cmdline_read(str
* 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;

@@ -272,8 +272,7 @@ static ssize_t proc_pid_cmdline_read(str
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)
@@ -308,8 +307,7 @@ static ssize_t proc_pid_cmdline_read(str
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)
@@ -358,8 +356,7 @@ 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)
@@ -871,7 +868,7 @@ static ssize_t mem_rw(struct file *file,
unsigned long addr = *ppos;
ssize_t copied;
char *page;
- unsigned int flags = FOLL_FORCE;
+ unsigned int flags;

if (!mm)
return 0;
@@ -884,6 +881,8 @@ static ssize_t mem_rw(struct file *file,
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;

@@ -1007,8 +1006,7 @@ static ssize_t environ_read(struct file
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;