Re: [PATCH try #4] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 8 May 2015 15:28:05 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:

> /proc/$PID/cmdline truncates output at PAGE_SIZE. It is easy to see with
> 
> 	$ cat /proc/self/cmdline $(seq 1037) 2>/dev/null
> 
> However, command line size was never limited to PAGE_SIZE but to 128 KB and
> relatively recently limitation was removed altogether.
> 
> People noticed and ask questions:
> http://stackoverflow.com/questions/199130/how-do-i-increase-the-proc-pid-cmdline-4096-byte-limit
> 
> seq file interface is not OK, because it kmalloc's for whole output and
> open + read(, 1) + sleep will pin arbitrary amounts of kernel memory.
> To not do that, limit must be imposed which is incompatible with
> arbitrary sized command lines.
> 
> I apologize for hairy code, but this it direct consequence of command line
> layout in memory and hacks to support things like "init [3]".
> 
> The loops are "unrolled" otherwise it is either macros which hide
> control flow or functions with 7-8 arguments with equal line count.
> 
> There should be real setproctitle(2) or something.
> 
> ...
>
>  fs/proc/base.c |  203 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 194 insertions(+), 9 deletions(-)

I still hate your patch!


Also, dude.  i386:

In file included from include/asm-generic/bug.h:13:0,
                 from ./arch/x86/include/asm/bug.h:35,
                 from include/linux/bug.h:4,
                 from include/linux/thread_info.h:11,
                 from ./arch/x86/include/asm/uaccess.h:8,
                 from fs/proc/base.c:50:
fs/proc/base.c: In function 'proc_pid_cmdline_read':
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:600:9: note: in definition of macro 'min'
  typeof(x) _min1 = (x);   \
         ^
include/linux/kernel.h:611:38: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                                      ^
fs/proc/base.c:265:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:600:21: note: in definition of macro 'min'
  typeof(x) _min1 = (x);   \
                     ^
include/linux/kernel.h:611:38: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                                      ^
fs/proc/base.c:265:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:611:23: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                       ^
fs/proc/base.c:265:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:600:9: note: in definition of macro 'min'
  typeof(x) _min1 = (x);   \
         ^
include/linux/kernel.h:611:38: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                                      ^
fs/proc/base.c:300:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:600:21: note: in definition of macro 'min'
  typeof(x) _min1 = (x);   \
                     ^
include/linux/kernel.h:611:38: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                                      ^
fs/proc/base.c:300:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:611:23: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                       ^
fs/proc/base.c:300:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:600:9: note: in definition of macro 'min'
  typeof(x) _min1 = (x);   \
         ^
include/linux/kernel.h:611:38: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                                      ^
fs/proc/base.c:349:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:600:21: note: in definition of macro 'min'
  typeof(x) _min1 = (x);   \
                     ^
include/linux/kernel.h:611:38: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                                      ^
fs/proc/base.c:349:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^
include/linux/kernel.h:602:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_min1 == &_min2);  \
                 ^
include/linux/kernel.h:611:23: note: in expansion of macro 'min'
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
                       ^
fs/proc/base.c:349:13: note: in expansion of macro 'min3'
    _count = min3(count, len, PAGE_SIZE);
             ^

--- a/fs/proc/base.c~proc-fix-page_size-limit-of-proc-pid-cmdline-fix
+++ a/fs/proc/base.c
@@ -197,11 +197,12 @@ static int proc_root_link(struct dentry
 }
 
 static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
-				     size_t count, loff_t *pos)
+				     size_t _count, loff_t *pos)
 {
 	struct task_struct *tsk;
 	struct mm_struct *mm;
 	char *page;
+	unsigned long count = _count;
 	unsigned long arg_start, arg_end, env_start, env_end;
 	unsigned long len1, len2, len;
 	unsigned long p;
_