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Commit 8c829622 authored by yonghua zheng's avatar yonghua zheng Committed by Linus Torvalds
Browse files

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: default avatarYonghua Zheng <younghua.zheng@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus 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;