[PATCH v2] md/bitmap: don't set sb values if can't pass sanity check

[PATCH v2] md/bitmap: don't set sb values if can't pass sanity check

[Heming Zhao]

If bitmap area contains invalid data, kernel will crash then mdadm
triggers "Segmentation fault".
This is cluster-md speical bug. In non-clustered env, mdadm will
handle broken metadata case. In clustered array, only kernel space
handles bitmap slot info. But even this bug only happened in clustered
env, current sanity check is wrong, the code should be changed.

How to trigger: (faulty injection)

dd if=/dev/zero bs=1M count=1 oflag=direct of=/dev/sda
dd if=/dev/zero bs=1M count=1 oflag=direct of=/dev/sdb
mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sda /dev/sdb
mdadm -Ss
echo aaa > magic.txt
 == below modifying slot 2 bitmap data ==
dd if=magic.txt of=/dev/sda seek=16384 bs=1 count=3 <== destroy magic
dd if=/dev/zero of=/dev/sda seek=16436 bs=1 count=4 <== ZERO chunksize
mdadm -A /dev/md0 /dev/sda /dev/sdb
 == kernel crashes. mdadm outputs "Segmentation fault" ==

Crash log:

kernel: md: md0 stopped.
kernel: md/raid1:md0: not clean -- starting background reconstruction
kernel: md/raid1:md0: active with 2 out of 2 mirrors
kernel: dlm: ... ...
kernel: md-cluster: Joined cluster 44810aba-38bb-e6b8-daca-bc97a0b254aa slot 1
kernel: md0: invalid bitmap file superblock: bad magic
kernel: md_bitmap_copy_from_slot can't get bitmap from slot 2
kernel: md-cluster: Could not gather bitmaps from slot 2
kernel: divide error: 0000 [#1] SMP NOPTI
kernel: CPU: 0 PID: 1603 Comm: mdadm Not tainted 5.14.6-1-default
kernel: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
kernel: RIP: 0010:md_bitmap_create+0x1d1/0x850 [md_mod]
kernel: RSP: 0018:ffffc22ac0843ba0 EFLAGS: 00010246
kernel: ... ...
kernel: Call Trace:
kernel:  ? dlm_lock_sync+0xd0/0xd0 [md_cluster 77fe..7a0]
kernel:  md_bitmap_copy_from_slot+0x2c/0x290 [md_mod 24ea..d3a]
kernel:  load_bitmaps+0xec/0x210 [md_cluster 77fe..7a0]
kernel:  md_bitmap_load+0x81/0x1e0 [md_mod 24ea..d3a]
kernel:  do_md_run+0x30/0x100 [md_mod 24ea..d3a]
kernel:  md_ioctl+0x1290/0x15a0 [md_mod 24ea....d3a]
kernel:  ? mddev_unlock+0xaa/0x130 [md_mod 24ea..d3a]
kernel:  ? blkdev_ioctl+0xb1/0x2b0
kernel:  block_ioctl+0x3b/0x40
kernel:  __x64_sys_ioctl+0x7f/0xb0
kernel:  do_syscall_64+0x59/0x80
kernel:  ? exit_to_user_mode_prepare+0x1ab/0x230
kernel:  ? syscall_exit_to_user_mode+0x18/0x40
kernel:  ? do_syscall_64+0x69/0x80
kernel:  entry_SYSCALL_64_after_hwframe+0x44/0xae
kernel: RIP: 0033:0x7f4a15fa722b
kernel: ... ...
kernel: ---[ end trace 8afa7612f559c868 ]---
kernel: RIP: 0010:md_bitmap_create+0x1d1/0x850 [md_mod]

Signed-off-by: Heming Zhao <heming.zhao@suse.com>
---
v2: * revise commit log
      - change mdadm "FPE" error to "Segmentation fault" error
        ("FPE" belongs to another issue)
      - add kernel crash log
    * modify a comment style to follow code rule
    * change strlcpy to strscpy for strlcpy is marked as deprecated in
      Documentation/process/deprecated.rst
      - note: strlcpy() still exists in md.c & md-cluster.c
---
 drivers/md/md-bitmap.c | 43 ++++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index bfd6026d7809..1e3ddc2619bd 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -635,19 +635,6 @@ static int md_bitmap_read_sb(struct bitmap *bitmap)
 	err = -EINVAL;
 	sb = kmap_atomic(sb_page);
 
-	chunksize = le32_to_cpu(sb->chunksize);
-	daemon_sleep = le32_to_cpu(sb->daemon_sleep) * HZ;
-	write_behind = le32_to_cpu(sb->write_behind);
-	sectors_reserved = le32_to_cpu(sb->sectors_reserved);
-	/* Setup nodes/clustername only if bitmap version is
-	 * cluster-compatible
-	 */
-	if (sb->version == cpu_to_le32(BITMAP_MAJOR_CLUSTERED)) {
-		nodes = le32_to_cpu(sb->nodes);
-		strlcpy(bitmap->mddev->bitmap_info.cluster_name,
-				sb->cluster_name, 64);
-	}
-
 	/* verify that the bitmap-specific fields are valid */
 	if (sb->magic != cpu_to_le32(BITMAP_MAGIC))
 		reason = "bad magic";
@@ -668,6 +655,20 @@ static int md_bitmap_read_sb(struct bitmap *bitmap)
 		goto out;
 	}
 
+	chunksize = le32_to_cpu(sb->chunksize);
+	daemon_sleep = le32_to_cpu(sb->daemon_sleep) * HZ;
+	write_behind = le32_to_cpu(sb->write_behind);
+	sectors_reserved = le32_to_cpu(sb->sectors_reserved);
+	/*
+	 * Setup nodes/clustername only if bitmap version is
+	 * cluster-compatible
+	 */
+	if (sb->version == cpu_to_le32(BITMAP_MAJOR_CLUSTERED)) {
+		nodes = le32_to_cpu(sb->nodes);
+		strscpy(bitmap->mddev->bitmap_info.cluster_name,
+				sb->cluster_name, 64);
+	}
+
 	/* keep the array size field of the bitmap superblock up to date */
 	sb->sync_size = cpu_to_le64(bitmap->mddev->resync_max_sectors);
 
@@ -695,14 +696,14 @@ static int md_bitmap_read_sb(struct bitmap *bitmap)
 	if (le32_to_cpu(sb->version) == BITMAP_MAJOR_HOSTENDIAN)
 		set_bit(BITMAP_HOSTENDIAN, &bitmap->flags);
 	bitmap->events_cleared = le64_to_cpu(sb->events_cleared);
-	strlcpy(bitmap->mddev->bitmap_info.cluster_name, sb->cluster_name, 64);
+	strscpy(bitmap->mddev->bitmap_info.cluster_name, sb->cluster_name, 64);
 	err = 0;
 
 out:
 	kunmap_atomic(sb);
-	/* Assigning chunksize is required for "re_read" */
-	bitmap->mddev->bitmap_info.chunksize = chunksize;
 	if (err == 0 && nodes && (bitmap->cluster_slot < 0)) {
+		/* Assigning chunksize is required for "re_read" */
+		bitmap->mddev->bitmap_info.chunksize = chunksize;
 		err = md_setup_cluster(bitmap->mddev, nodes);
 		if (err) {
 			pr_warn("%s: Could not setup cluster service (%d)\n",
@@ -717,10 +718,12 @@ static int md_bitmap_read_sb(struct bitmap *bitmap)
 out_no_sb:
 	if (test_bit(BITMAP_STALE, &bitmap->flags))
 		bitmap->events_cleared = bitmap->mddev->events;
-	bitmap->mddev->bitmap_info.chunksize = chunksize;
-	bitmap->mddev->bitmap_info.daemon_sleep = daemon_sleep;
-	bitmap->mddev->bitmap_info.max_write_behind = write_behind;
-	bitmap->mddev->bitmap_info.nodes = nodes;
+	if (err == 0) {
+		bitmap->mddev->bitmap_info.chunksize = chunksize;
+		bitmap->mddev->bitmap_info.daemon_sleep = daemon_sleep;
+		bitmap->mddev->bitmap_info.max_write_behind = write_behind;
+		bitmap->mddev->bitmap_info.nodes = nodes;
+	}
 	if (bitmap->mddev->bitmap_info.space == 0 ||
 	    bitmap->mddev->bitmap_info.space > sectors_reserved)
 		bitmap->mddev->bitmap_info.space = sectors_reserved;
-- 
2.34.1

Re: [PATCH v2] md/bitmap: don't set sb values if can't pass sanity check

[heming.zhao]

On 3/29/22 15:27, Heming Zhao wrote:
> If bitmap area contains invalid data, kernel will crash then mdadm
> triggers "Segmentation fault".
> This is cluster-md speical bug. In non-clustered env, mdadm will
> handle broken metadata case. In clustered array, only kernel space
> handles bitmap slot info. But even this bug only happened in clustered
> env, current sanity check is wrong, the code should be changed> ... ...
> 
> Signed-off-by: Heming Zhao <heming.zhao@suse.com>
> ---
> v2: * revise commit log
>        - change mdadm "FPE" error to "Segmentation fault" error
>          ("FPE" belongs to another issue)
>        - add kernel crash log
>      * modify a comment style to follow code rule
>      * change strlcpy to strscpy for strlcpy is marked as deprecated in
>        Documentation/process/deprecated.rst
>        - note: strlcpy() still exists in md.c & md-cluster.c

Please note, beside Guoqing's review comments, I added new code change : strlcpy() => strscpy()

- Heming