From: Minchan Kim <minchan@xxxxxxxxxx> Subject: drivers/block/zram/zram_drv.c: fix idle/writeback string compare 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 Link: http://lkml.kernel.org/r/20190319231911.145968-1-minchan@xxxxxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> [5.0] Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Reported-by: Makoto Wu <makotowu@xxxxxxxxxx> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/block/zram/zram_drv.c | 32 ++++++-------------------------- 1 file changed, 6 insertions(+), 26 deletions(-) --- a/drivers/block/zram/zram_drv.c~zram-fix-idle-writeback-string-compare +++ a/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); _
