proc: deduplicate /proc/*/cmdline implementation

Code can be sonsolidated if a dummy region of 0 length is used in normal
case of \0-separated command line:

1) [arg_start, arg_end) + [dummy len=0]
2) [arg_start, arg_end) + [env_start, env_end)

Link: http://lkml.kernel.org/r/20180221193335.GB28678@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 3fcca77..3954f50 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -213,9 +213,12 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
        char *page;
        unsigned long count = _count;
        unsigned long arg_start, arg_end, env_start, env_end;
-       unsigned long len1, len2, len;
-       unsigned long p;
+       unsigned long len1, len2;
        char __user *buf0 = buf;
+       struct {
+               unsigned long p;
+               unsigned long len;
+       } cmdline[2];
        char c;
        int rv;
 
@@ -264,43 +267,21 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
        if (access_remote_vm(mm, arg_end - 1, &c, 1, FOLL_ANON) != 1)
                goto end;
 
+       cmdline[0].p = arg_start;
+       cmdline[0].len = len1;
        if (c == '\0') {
                /* Command line (set of strings) occupies whole ARGV. */
-               if (len1 <= *pos)
-                       goto end;
-
-               p = arg_start + *pos;
-               len = len1 - *pos;
-               while (count > 0 && len > 0) {
-                       unsigned int nr_read;
-
-                       nr_read = min3(count, len, PAGE_SIZE);
-                       nr_read = access_remote_vm(mm, p, page, nr_read, FOLL_ANON);
-                       if (nr_read == 0)
-                               goto end;
-
-                       if (copy_to_user(buf, page, nr_read)) {
-                               rv = -EFAULT;
-                               goto out_free_page;
-                       }
-
-                       p       += nr_read;
-                       len     -= nr_read;
-                       buf     += nr_read;
-                       count   -= nr_read;
-               }
+               cmdline[1].len = 0;
        } else {
                /*
                 * Command line (1 string) occupies ARGV and
                 * extends into ENVP.
                 */
-               struct {
-                       unsigned long p;
-                       unsigned long len;
-               } cmdline[2] = {
-                       { .p = arg_start, .len = len1 },
-                       { .p = env_start, .len = len2 },
-               };
+               cmdline[1].p = env_start;
+               cmdline[1].len = len2;
+       }
+
+       {
                loff_t pos1 = *pos;
                unsigned int i;
 
@@ -310,6 +291,9 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
                        i++;
                }
                while (i < 2) {
+                       unsigned long p;
+                       unsigned long len;
+
                        p = cmdline[i].p + pos1;
                        len = cmdline[i].len - pos1;
                        while (count > 0 && len > 0) {
@@ -324,7 +308,10 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
                                 * Command line can be shorter than whole ARGV
                                 * even if last "marker" byte says it is not.
                                 */
-                               nr_write = strnlen(page, nr_read);
+                               if (c == '\0')
+                                       nr_write = nr_read;
+                               else
+                                       nr_write = strnlen(page, nr_read);
 
                                if (copy_to_user(buf, page, nr_write)) {
                                        rv = -EFAULT;