Commit 8c829622 authored Aug 13, 2013 by yonghua zheng Committed by Linus Torvalds Aug 13, 2013

fs/proc/task_mmu.c: fix buffer overflow in add_page_map()



Recently we met quite a lot of random kernel panic issues after enabling
CONFIG_PROC_PAGE_MONITOR.  After debuggind we found this has something
to do with following bug in pagemap:

In struct pagemapread:

  struct pagemapread {
      int pos, len;
      pagemap_entry_t *buffer;
      bool v2;
  };

pos is number of PM_ENTRY_BYTES in buffer, but len is the size of
buffer, it is a mistake to compare pos and len in add_page_map() for
checking buffer is full or not, and this can lead to buffer overflow and
random kernel panic issue.

Correct len to be total number of PM_ENTRY_BYTES in buffer.

[akpm@linux-foundation.org: document pagemapread.pos and .len units, fix PM_ENTRY_BYTES definition]
Signed-off-by: Yonghua Zheng <younghua.zheng@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 57a1a197

fs/proc/task_mmu.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -868,7 +868,7 @@ typedef struct {
		} pagemap_entry_t;

		struct pagemapread {
		int pos, len;
		int pos, len; /* units: PM_ENTRY_BYTES, not bytes */
		pagemap_entry_t *buffer;
		bool v2;
		};
		@@ -876,7 +876,7 @@ struct pagemapread {
		#define PAGEMAP_WALK_SIZE (PMD_SIZE)
		#define PAGEMAP_WALK_MASK (PMD_MASK)

		#define PM_ENTRY_BYTES sizeof(u64)
		#define PM_ENTRY_BYTES sizeof(pagemap_entry_t)
		#define PM_STATUS_BITS 3
		#define PM_STATUS_OFFSET (64 - PM_STATUS_BITS)
		#define PM_STATUS_MASK (((1LL << PM_STATUS_BITS) - 1) << PM_STATUS_OFFSET)
		@@ -1127,8 +1127,8 @@ static ssize_t pagemap_read(struct file file, char __user buf,
		goto out_task;

		pm.v2 = soft_dirty_cleared;
		pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
		pm.buffer = kmalloc(pm.len, GFP_TEMPORARY);
		pm.len = (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
		pm.buffer = kmalloc(pm.len * PM_ENTRY_BYTES, GFP_TEMPORARY);
		ret = -ENOMEM;
		if (!pm.buffer)
		goto out_task;

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