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* [PATCH] zram: fix idle/writeback string compare
@ 2019-03-19 23:19 Minchan Kim
  2019-03-20  1:55 ` Sergey Senozhatsky
  0 siblings, 1 reply; 2+ messages in thread
From: Minchan Kim @ 2019-03-19 23:19 UTC (permalink / raw)
  To: Andrew Morton; +Cc: Sergey Senozhatsky, LKML, Minchan Kim, stable, Makoto Wu

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.

[  280.626730] c0 1314   ==================================================================
[  280.626855] c0 1314   BUG: KASAN: slab-out-of-bounds in strscpy+0x68/0x154
[  280.626896] c0 1314   Read of size 8 at addr ffffffc0c3495a00 by task system_server/1314
[  280.626921] c0 1314
..
[  280.627041] c0 1314   Call trace:
[  280.627097] c0 1314   [<ffffff90080902b8>] dump_backtrace+0x0/0x6bc
[  280.627142] c0 1314   [<ffffff90080902ac>] show_stack+0x20/0x2c
[  280.627193] c0 1314   [<ffffff900871fa90>] dump_stack+0xfc/0x140
[  280.627250] c0 1314   [<ffffff90083364ec>] print_address_description+0x80/0x2d8
[  280.627294] c0 1314   [<ffffff9008336b48>] kasan_report_error+0x198/0x1fc
[  280.627335] c0 1314   [<ffffff90083369b0>] kasan_report_error+0x0/0x1fc
[  280.627376] c0 1314   [<ffffff9008335c1c>] __asan_load8+0x1b0/0x1b8
[  280.627415] c0 1314   [<ffffff900872fb6c>] strscpy+0x68/0x154
[  280.627465] c0 1314   [<ffffff9008ceca44>] idle_store+0xc4/0x34c
[  280.627511] c0 1314   [<ffffff9008c91a98>] dev_attr_store+0x50/0x6c
[  280.627558] c0 1314   [<ffffff900845602c>] sysfs_kf_write+0x98/0xb4
[  280.627596] c0 1314   [<ffffff9008453d20>] kernfs_fop_write+0x198/0x260
[  280.627642] c0 1314   [<ffffff90083578b4>] __vfs_write+0x10c/0x338
[  280.627684] c0 1314   [<ffffff9008357dac>] vfs_write+0x114/0x238
[  280.627726] c0 1314   [<ffffff9008358100>] SyS_write+0xc8/0x168
[  280.627767] c0 1314   [<ffffff900808425c>] __sys_trace_return+0x0/0x4
[  280.627791] c0 1314
[  280.627824] c0 1314   Allocated by task 1314:
[  280.627866] c0 1314    kasan_kmalloc+0xe0/0x1ac
[  280.627903] c0 1314    __kmalloc+0x280/0x318
[  280.627938] c0 1314    kernfs_fop_write+0xac/0x260
[  280.627980] c0 1314    __vfs_write+0x10c/0x338
[  280.628020] c0 1314    vfs_write+0x114/0x238
[  280.628061] c0 1314    SyS_write+0xc8/0x168
[  280.628098] c0 1314    __sys_trace_return+0x0/0x4
[  280.628125] c0 1314
[  280.628154] c0 1314   Freed by task 2855:
[  280.628194] c0 1314    kasan_slab_free+0xb8/0x194
[  280.628229] c0 1314    kfree+0x138/0x630
[  280.628266] c0 1314    kernfs_put_open_node+0x10c/0x124
[  280.628302] c0 1314    kernfs_fop_release+0xd8/0x114
[  280.628336] c0 1314    __fput+0x130/0x2a4
[  280.628370] c0 1314    ____fput+0x1c/0x28
[  280.628410] c0 1314    task_work_run+0x16c/0x1c8
[  280.628449] c0 1314    do_notify_resume+0x2bc/0x107c
[  280.628483] c0 1314    work_pending+0x8/0x10
[  280.628506] c0 1314
[  280.628542] c0 1314   The buggy address belongs to the object at ffffffc0c3495a00
[  280.628542] c0 1314    which belongs to the cache kmalloc-128 of size 128
[  280.628597] c0 1314   The buggy address is located 0 bytes inside of
[  280.628597] c0 1314    128-byte region [ffffffc0c3495a00, ffffffc0c3495a80)
[  280.628642] c0 1314   The buggy address belongs to the page:
[  280.628680] c0 1314   page:ffffffbf030d2500 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
[  280.628721] c0 1314   flags: 0x4000000000010200(slab|head)
[  280.628748] c0 1314   page dumped because: kasan: bad access detected
[  280.628772] c0 1314
[  280.628797] c0 1314   Memory state around the buggy address:
[  280.628840] c0 1314    ffffffc0c3495900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[  280.628874] c0 1314    ffffffc0c3495980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[  280.628909] c0 1314   >ffffffc0c3495a00: 04 fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[  280.628935] c0 1314                      ^
[  280.628969] c0 1314    ffffffc0c3495a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[  280.629005] c0 1314    ffffffc0c3495b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Cc: <stable@vger.kernel.org>	[5.0]
Reported-by: Makoto Wu <makotowu@google.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/block/zram/zram_drv.c | 32 ++++++--------------------------
 1 file changed, 6 insertions(+), 26 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index e7a5f1d1c3141..399cad7daae77 100644
--- 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 *dev,
 	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 device *dev,
 	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);
-- 
2.21.0.225.g810b269d1ac-goog


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH] zram: fix idle/writeback string compare
  2019-03-19 23:19 [PATCH] zram: fix idle/writeback string compare Minchan Kim
@ 2019-03-20  1:55 ` Sergey Senozhatsky
  0 siblings, 0 replies; 2+ messages in thread
From: Sergey Senozhatsky @ 2019-03-20  1:55 UTC (permalink / raw)
  To: Minchan Kim; +Cc: Andrew Morton, Sergey Senozhatsky, LKML, stable, Makoto Wu

On (03/20/19 08:19), Minchan Kim wrote:
> Cc: <stable@vger.kernel.org>	[5.0]
> Reported-by: Makoto Wu <makotowu@google.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

> +++ b/drivers/block/zram/zram_drv.c
> @@ -290,18 +290,8 @@ static ssize_t idle_store(struct device *dev,
>  	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;
[..]

That's a good improvement of the code.

	-ss

^ permalink raw reply	[flat|nested] 2+ messages in thread

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