1 files changed, 75 insertions, 57 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 77eb628ecc7f..ebea9501afb8 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -209,12 +209,53 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
         return result;
 }
 
+/*
+ * If the user used setproctitle(), we just get the string from
+ * user space at arg_start, and limit it to a maximum of one page.
+ */
+static ssize_t get_mm_proctitle(struct mm_struct *mm, char __user *buf,
+                                size_t count, unsigned long pos,
+                                unsigned long arg_start)
+{
+        char *page;
+        int ret, got;
+
+        if (pos >= PAGE_SIZE)
+                return 0;
+
+        page = (char *)__get_free_page(GFP_KERNEL);
+        if (!page)
+                return -ENOMEM;
+
+        ret = 0;
+        got = access_remote_vm(mm, arg_start, page, PAGE_SIZE, FOLL_ANON);
+        if (got > 0) {
+                int len = strnlen(page, got);
+
+                /* Include the NUL character if it was found */
+                if (len < got)
+                        len++;
+
+                if (len > pos) {
+                        len -= pos;
+                        if (len > count)
+                                len = count;
+                        len -= copy_to_user(buf, page+pos, len);
+                        if (!len)
+                                len = -EFAULT;
+                        ret = len;
+                }
+        }
+        free_page((unsigned long)page);
+        return ret;
+}
+
 static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
                               size_t count, loff_t *ppos)
 {
         unsigned long arg_start, arg_end, env_start, env_end;
         unsigned long pos, len;
-        char *page;
+        char *page, c;
 
         /* Check if process spawned far enough to have cmdline. */
         if (!mm->env_end)
@@ -231,28 +272,42 @@ static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
                 return 0;
 
         /*
-         * We have traditionally allowed the user to re-write
-         * the argument strings and overflow the end result
-         * into the environment section. But only do that if
-         * the environment area is contiguous to the arguments.
+         * We allow setproctitle() to overwrite the argument
+         * strings, and overflow past the original end. But
+         * only when it overflows into the environment area.
          */
-        if (env_start != arg_end || env_start >= env_end)
+        if (env_start != arg_end || env_end < env_start)
                 env_start = env_end = arg_end;
-
-        /* .. and limit it to a maximum of one page of slop */
-        if (env_end >= arg_end + PAGE_SIZE)
-                env_end = arg_end + PAGE_SIZE - 1;
+        len = env_end - arg_start;
 
         /* We're not going to care if "*ppos" has high bits set */
-        pos = arg_start + *ppos;
-
-        /* .. but we do check the result is in the proper range */
-        if (pos < arg_start || pos >= env_end)
+        pos = *ppos;
+        if (pos >= len)
                 return 0;
+        if (count > len - pos)
+                count = len - pos;
+        if (!count)
+                return 0;
+
+        /*
+         * Magical special case: if the argv[] end byte is not
+         * zero, the user has overwritten it with setproctitle(3).
+         *
+         * Possible future enhancement: do this only once when
+         * pos is 0, and set a flag in the 'struct file'.
+         */
+        if (access_remote_vm(mm, arg_end-1, &c, 1, FOLL_ANON) == 1 && c)
+                return get_mm_proctitle(mm, buf, count, pos, arg_start);
 
-        /* .. and we never go past env_end */
-        if (env_end - pos < count)
-                count = env_end - pos;
+        /*
+         * For the non-setproctitle() case we limit things strictly
+         * to the [arg_start, arg_end[ range.
+         */
+        pos += arg_start;
+        if (pos < arg_start || pos >= arg_end)
+                return 0;
+        if (count > arg_end - pos)
+                count = arg_end - pos;
 
         page = (char *)__get_free_page(GFP_KERNEL);
         if (!page)
@@ -262,48 +317,11 @@ static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
         while (count) {
                 int got;
                 size_t size = min_t(size_t, PAGE_SIZE, count);
-                long offset;
 
-                /*
-                 * Are we already starting past the official end?
-                 * We always include the last byte that is *supposed*
-                 * to be NUL
-                 */
-                offset = (pos >= arg_end) ? pos - arg_end + 1 : 0;
-
-                got = access_remote_vm(mm, pos - offset, page, size + offset, FOLL_ANON);
-                if (got <= offset)
+                got = access_remote_vm(mm, pos, page, size, FOLL_ANON);
+                if (got <= 0)
                         break;
-                got -= offset;
-
-                /* Don't walk past a NUL character once you hit arg_end */
-                if (pos + got >= arg_end) {
-                        int n = 0;
-
-                        /*
-                         * If we started before 'arg_end' but ended up
-                         * at or after it, we start the NUL character
-                         * check at arg_end-1 (where we expect the normal
-                         * EOF to be).
-                         *
-                         * NOTE! This is smaller than 'got', because
-                         * pos + got >= arg_end
-                         */
-                        if (pos < arg_end)
-                                n = arg_end - pos - 1;
-
-                        /* Cut off at first NUL after 'n' */
-                        got = n + strnlen(page+n, offset+got-n);
-                        if (got < offset)
-                                break;
-                        got -= offset;
-
-                        /* Include the NUL if it existed */
-                        if (got < size)
-                                got++;
-                }
-
-                got -= copy_to_user(buf, page+offset, got);
+                got -= copy_to_user(buf, page, got);
                 if (unlikely(!got)) {
                         if (!len)
                                 len = -EFAULT;