linux-kernel - [PATCH v4 2/7] zram: fix double free backing device

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Date:   Mon,  3 Dec 2018 11:40:40 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Joey Pabalinas <joeypabalinas@...il.com>,
        Minchan Kim <minchan@...nel.org>, stable@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [PATCH v4 2/7] zram: fix double free backing device

If blkdev_get fails, we shouldn't do blkdev_put. Otherwise,
kernel emits below log. This patch fixes it.

[   31.073006] WARNING: CPU: 0 PID: 1893 at fs/block_dev.c:1828 blkdev_put+0x105/0x120
[   31.075104] Modules linked in:
[   31.075898] CPU: 0 PID: 1893 Comm: swapoff Not tainted 4.19.0+ #453
[   31.077484] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[   31.079589] RIP: 0010:blkdev_put+0x105/0x120
[   31.080606] Code: 48 c7 80 a0 00 00 00 00 00 00 00 48 c7 c7 40 e7 40 96 e8 6e 47 73 00 48 8b bb e0 00 00 00 e9 2c ff ff ff 0f 0b e9 75 ff ff ff <0f> 0b e9 5a ff ff ff 48 c7 80 a0 00 00 00 00 00 00 00 eb 87 0f 1f
[   31.085080] RSP: 0018:ffffb409005c7ed0 EFLAGS: 00010297
[   31.086383] RAX: ffff9779fe5a8040 RBX: ffff9779fbc17300 RCX: 00000000b9fc37a4
[   31.088105] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffffffff9640e740
[   31.089850] RBP: ffff9779fbc17318 R08: ffffffff95499a89 R09: 0000000000000004
[   31.091201] R10: ffffb409005c7e50 R11: 7a9ef6088ff4d4a1 R12: 0000000000000083
[   31.092276] R13: ffff9779fe607b98 R14: 0000000000000000 R15: ffff9779fe607a38
[   31.093355] FS:  00007fc118d9b840(0000) GS:ffff9779fc600000(0000) knlGS:0000000000000000
[   31.094582] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   31.095541] CR2: 00007fc11894b8dc CR3: 00000000339f6001 CR4: 0000000000160ef0
[   31.096781] Call Trace:
[   31.097212]  __x64_sys_swapoff+0x46d/0x490
[   31.097914]  do_syscall_64+0x5a/0x190
[   31.098550]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   31.099402] RIP: 0033:0x7fc11843ec27
[   31.100013] Code: 73 01 c3 48 8b 0d 71 62 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a8 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 41 62 2c 00 f7 d8 64 89 01 48
[   31.103149] RSP: 002b:00007ffdf69be648 EFLAGS: 00000206 ORIG_RAX: 00000000000000a8
[   31.104425] RAX: ffffffffffffffda RBX: 00000000011d98c0 RCX: 00007fc11843ec27
[   31.105627] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 00000000011d98c0
[   31.106847] RBP: 0000000000000001 R08: 00007ffdf69be690 R09: 0000000000000001
[   31.108038] R10: 00000000000002b1 R11: 0000000000000206 R12: 0000000000000001
[   31.109231] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   31.110433] irq event stamp: 4466
[   31.111001] hardirqs last  enabled at (4465): [<ffffffff953ebd43>] __free_pages_ok+0x1e3/0x490
[   31.112437] hardirqs last disabled at (4466): [<ffffffff95201b7a>] trace_hardirqs_off_thunk+0x1a/0x1c
[   31.113973] softirqs last  enabled at (3420): [<ffffffff95e00333>] __do_softirq+0x333/0x446
[   31.115364] softirqs last disabled at (3407): [<ffffffff9527aee1>] irq_exit+0xd1/0xe0

Cc: stable@...r.kernel.org # 4.14+
Reviewed-by: Joey Pabalinas <joeypabalinas@...il.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 drivers/block/zram/zram_drv.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 21a7046958a3..d1459cc1159f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -387,8 +387,10 @@ static ssize_t backing_dev_store(struct device *dev,
 
 	bdev = bdgrab(I_BDEV(inode));
 	err = blkdev_get(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, zram);
-	if (err < 0)
+	if (err < 0) {
+		bdev = NULL;
 		goto out;
+	}
 
 	nr_pages = i_size_read(inode) >> PAGE_SHIFT;
 	bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long);
-- 
2.20.0.rc1.387.gf8505762e3-goog