[PATCH] proc: Fix the issue of proc_mem_open returning NULL

[Penglei Jiang]

The following functions call proc_mem_open but do not handle the case
where it returns NULL:

  __mem_open in fs/proc/base.c
  proc_maps_open in fs/proc/task_mmu.c
  smaps_rollup_open in fs/proc/task_mmu.c
  pagemap_open in fs/proc/task_mmu.c
  maps_open in fs/proc/task_nommu.c

The following reported bugs may be related to this issue:

  https://lore.kernel.org/all/000000000000f52642060d4e3750@xxxxxxxxxx
  https://lore.kernel.org/all/0000000000001bc4a00612d9a7f4@xxxxxxxxxx

Fix:

Modify proc_mem_open to return an error code in case of errors, instead
of returning NULL.

Signed-off-by: Penglei Jiang <superman.xpt@xxxxxxxxx>
---
 fs/proc/base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index cd89e956c322..b5e7317cf0dc 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -840,7 +840,7 @@ struct mm_struct *proc_mem_open(struct inode *inode, unsigned int mode)
 	put_task_struct(task);
 
 	if (IS_ERR(mm))
-		return mm == ERR_PTR(-ESRCH) ? NULL : mm;
+		return mm;
 
 	/* ensure this mm_struct can't be freed */
 	mmgrab(mm);
-- 
2.17.1