[PATCH] mm/backing-dev.c: check user buffer length before copy data to the related user buffer.

[Chen Gang <gang.chen@asianux.com>]

'*lenp' may be less than "sizeof(kbuf)", need check it before the next
copy_to_user().

pdflush_proc_obsolete() is called by sysctl which 'procname' is
"nr_pdflush_threads", if the user passes buffer length less than
"sizeof(kbuf)", it will cause issue.


Signed-off-by: Chen Gang <gang.chen@asianux.com>
---
 mm/backing-dev.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index e04454c..2674671 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -649,7 +649,7 @@ int pdflush_proc_obsolete(struct ctl_table *table, int write,
 {
 	char kbuf[] = "0\n";
 
-	if (*ppos) {
+	if (*ppos || *lenp < sizeof(kbuf)) {
 		*lenp = 0;
 		return 0;
 	}
-- 
1.7.7.6

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