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Subject[PATCH 5.0 102/146] drivers/block/zram/zram_drv.c: fix idle/writeback string compare
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Minchan Kim <minchan@kernel.org>

commit 0bc9f5d14a93971c6cd9c0d81b0fc154fc54c65d upstream.

Makoto report a below KASAN error: zram does out-of-bounds read. Because
strscpy copies from source up to count bytes unconditionally. It could
cause out-of-bounds read on next object in slab.

To prevent it, use strlcpy which checks source's length automatically.

BUG: KASAN: slab-out-of-bounds in strscpy+0x68/0x154
Read of size 8 at addr ffffffc0c3495a00 by task system_server/1314
..
Call trace:
strscpy+0x68/0x154
idle_store+0xc4/0x34c
dev_attr_store+0x50/0x6c
sysfs_kf_write+0x98/0xb4
kernfs_fop_write+0x198/0x260
__vfs_write+0x10c/0x338
vfs_write+0x114/0x238
SyS_write+0xc8/0x168
__sys_trace_return+0x0/0x4

Allocated by task 1314:
__kmalloc+0x280/0x318
kernfs_fop_write+0xac/0x260
__vfs_write+0x10c/0x338
vfs_write+0x114/0x238
SyS_write+0xc8/0x168
__sys_trace_return+0x0/0x4

Freed by task 2855:
kfree+0x138/0x630
kernfs_put_open_node+0x10c/0x124
kernfs_fop_release+0xd8/0x114
__fput+0x130/0x2a4
____fput+0x1c/0x28
task_work_run+0x16c/0x1c8
do_notify_resume+0x2bc/0x107c
work_pending+0x8/0x10

The buggy address belongs to the object at ffffffc0c3495a00
which belongs to the cache kmalloc-128 of size 128
The buggy address is located 0 bytes inside of
128-byte region [ffffffc0c3495a00, ffffffc0c3495a80)
The buggy address belongs to the page:
page:ffffffbf030d2500 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000010200(slab|head)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffffffc0c3495900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffffc0c3495980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffffffc0c3495a00: 04 fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffffffc0c3495a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffffffc0c3495b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Link: http://lkml.kernel.org/r/20190319231911.145968-1-minchan@kernel.org
Cc: <stable@vger.kernel.org> [5.0]
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Makoto Wu <makotowu@google.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/zram/zram_drv.c | 32 ++++++--------------------------
1 file changed, 6 insertions(+), 26 deletions(-)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -290,18 +290,8 @@ static ssize_t idle_store(struct device
struct zram *zram = dev_to_zram(dev);
unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
int index;
- char mode_buf[8];
- ssize_t sz;

- sz = strscpy(mode_buf, buf, sizeof(mode_buf));
- if (sz <= 0)
- return -EINVAL;
-
- /* ignore trailing new line */
- if (mode_buf[sz - 1] == '\n')
- mode_buf[sz - 1] = 0x00;
-
- if (strcmp(mode_buf, "all"))
+ if (!sysfs_streq(buf, "all"))
return -EINVAL;

down_read(&zram->init_lock);
@@ -635,25 +625,15 @@ static ssize_t writeback_store(struct de
struct bio bio;
struct bio_vec bio_vec;
struct page *page;
- ssize_t ret, sz;
- char mode_buf[8];
- int mode = -1;
+ ssize_t ret;
+ int mode;
unsigned long blk_idx = 0;

- sz = strscpy(mode_buf, buf, sizeof(mode_buf));
- if (sz <= 0)
- return -EINVAL;
-
- /* ignore trailing newline */
- if (mode_buf[sz - 1] == '\n')
- mode_buf[sz - 1] = 0x00;
-
- if (!strcmp(mode_buf, "idle"))
+ if (sysfs_streq(buf, "idle"))
mode = IDLE_WRITEBACK;
- else if (!strcmp(mode_buf, "huge"))
+ else if (sysfs_streq(buf, "huge"))
mode = HUGE_WRITEBACK;
-
- if (mode == -1)
+ else
return -EINVAL;

down_read(&zram->init_lock);

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