From: Weijie Yang <weijie.yang@xxxxxxxxxxx>
Subject: zram: avoid kunmap_atomic() of a NULL pointer
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>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN drivers/block/zram/zram_drv.c~zram-avoid-kunmap_atomic-a-null-pointer drivers/block/zram/zram_drv.c
--- a/drivers/block/zram/zram_drv.c~zram-avoid-kunmap_atomic-a-null-pointer
+++ a/drivers/block/zram/zram_drv.c
@@ -560,7 +560,8 @@ static int zram_bvec_write(struct zram *
}
if (page_zero_filled(uncmem)) {
- kunmap_atomic(user_mem);
+ if (user_mem)
+ kunmap_atomic(user_mem);
/* Free memory associated with this sector now. */
bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
zram_free_page(zram, index);
_
--
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