[PATCH 3.13.y-ckt 084/121] zram: avoid kunmap_atomic() of a NULL pointer

From: Kamal Mostafa
Date: Tue Dec 02 2014 - 14:47:33 EST

3.13.11-ckt12 -stable review patch. If anyone has any objections, please let me know.


From: Weijie Yang <weijie.yang@xxxxxxxxxxx>

commit c406515239376fc93a30d5d03192182160cbd3fb upstream.

zram could kunmap_atomic() a NULL pointer in a rare situation: a zram
page becomes a full-zeroed page after a partial write io. The current
code doesn't handle this case and performs kunmap_atomic() on a NULL
pointer, which panics the kernel.

This patch fixes this issue.

Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Dan Streetman <ddstreet@xxxxxxxx>
Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
Cc: Weijie Yang <weijie.yang.kh@xxxxxxxxx>
Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
drivers/staging/zram/zram_drv.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index e2f0add..63c2a5b 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -430,7 +430,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,

if (page_zero_filled(uncmem)) {
- kunmap_atomic(user_mem);
+ if (user_mem)
+ kunmap_atomic(user_mem);
/* Free memory associated with this sector now. */
zram_free_page(zram, index);


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