[PATCH v3 1/3] mm: Create utility function for accessing a tasks commandline value

William Roberts
2014-01-15T18:02:12Z

introduce get_cmdline() for retreiving the value of a processes
proc/self/cmdline value.

Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>

Signed-off-by: William Roberts <wroberts@tresys.com>
---
include/linux/mm.h | 1 +
mm/util.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 49 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3552717..01e7970 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1134,6 +1134,7 @@ void account_page_writeback(struct page *page);
int set_page_dirty(struct page *page);
int set_page_dirty_lock(struct page *page);
int clear_page_dirty_for_io(struct page *page);
+int get_cmdline(struct task_struct *task, char *buffer, int buflen);

/* Is the vma a continuation of the stack vma above it? */
static inline int vma_growsdown(struct vm_area_struct *vma, unsigned long addr)
diff --git a/mm/util.c b/mm/util.c
index 808f375..43b4419 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -413,6 +413,54 @@ unsigned long vm_commit_limit(void)
* sysctl_overcommit_ratio / 100) + total_swap_pages;
}

+/**
+ * get_cmdline() - copy the cmdline value to a buffer.
+ * @task: the task whose cmdline value to copy.
+ * @buffer: the buffer to copy to.
+ * @buflen: the length of the buffer. Larger cmdline values are truncated
+ * to this length.
+ * Returns the size of the cmdline field copied. Note that the copy does
+ * not guarantee an ending NULL byte.
+ */
+int get_cmdline(struct task_struct *task, char *buffer, int buflen)
+{
+ int res = 0;
+ unsigned int len;
+ struct mm_struct *mm = get_task_mm(task);
+ if (!mm)
+ goto out;
+ if (!mm->arg_end)
+ goto out_mm; /* Shh! No looking before we're done */
+
+ len = mm->arg_end - mm->arg_start;
+
+ if (len > buflen)
+ len = buflen;
+
+ res = access_process_vm(task, mm->arg_start, buffer, len, 0);
+
+ /*
+ * If the nul at the end of args has been overwritten, then
+ * assume application is using setproctitle(3).
+ */
+ if (res > 0 && buffer[res-1] != '\0' && len < buflen) {
+ len = strnlen(buffer, res);
+ if (len < res) {
+ res = len;
+ } else {
+ len = mm->env_end - mm->env_start;
+ if (len > buflen - res)
+ len = buflen - res;
+ res += access_process_vm(task, mm->env_start,
+ buffer+res, len, 0);
+ res = strnlen(buffer, res);
+ }
+ }
+out_mm:
+ mmput(mm);
+out:
+ return res;
+}

/* Tracepoints definitions. */
EXPORT_TRACEPOINT_SYMBOL(kmalloc);
--
1.7.9.5