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Subject[PATCH] LVM OOPS fixup
This patch fixes a longstanding user-exploitable OOPS in the LVM code.
I had hopes that in the last several months this fix would make it to the
stock kernel through official channels, but it has not.

The problem is in the LV_BMAP ioctl, which is similar to the FIBMAP ioctl,
so LILO can map kernel/initrd files from an LVM partition. The current
code incorrectly uses i_dev instead of i_rdev, so you reference an
invalid LV if /boot is not on the root fs. This causes an immediate NULL
pointer dereference. I have held back a patch from the LILO maintainer
to add LVM support to LILO until this is fixed in the mainline kernel,
and I don't want to wait any longer.

The patch changes the return value from LV_BMAP to be in blocks (as
the input value was) and not sectors (as lvm_map() returns). This
is how it has been in LVM CVS for a long time, and how FIBMAP also
works (which makes LILO on LVM happy).

The patch has been in the LVM CVS repository for many months and is also
in the -ac kernel. It also includes one other minor fix from LVM CVS
(SNAPSHOT_MIN_CHUNK) which should be added to the stock kernel as well,
not that there aren't lots more, but you have to start somewhere.

Cheers, Andreas

PS - lvm-devel is CC'd but for an unknown reason I have not gotten any
email from any of the LVM mailing lists in the last month or so,
so replies should be sent to me directly or to linux-kernel. Yes,
I'm still subscribed to the lists (according to the web subscription
page), and I tried emailing the list maintainer a couple of days ago
with alternate contact email addresses in case of problems.

diff -ru linux-2.4.6.orig/Documentation/ioctl-number.txt linux-2.4.6-aed/Documentation/ioctl-number.txt
--- linux-2.4.6.orig/Documentation/ioctl-number.txt Tue May 29 13:12:42 2001
+++ linux-2.4.6-aed/Documentation/ioctl-number.txt Mon Jun 4 17:16:42 2001
@@ -187,3 +187,5 @@
0xB1 00-1F PPPoX <>
0xCB 00-1F CBM serial IEC bus in development:
+0xFE 00-9F Logical Volume Manager <>
diff -ru linux-2.4.6.orig/drivers/md/lvm.c linux-2.4.6-aed/drivers/md/lvm.c
--- linux-2.4.6.orig/drivers/md/lvm.c Tue May 8 17:16:13 2001
+++ linux-2.4.6-aed/drivers/md/lvm.c Tue Jun 19 11:57:39 2001
@@ -988,6 +990,10 @@

case LV_BMAP:
/* turn logical block into (dev_t, block). non privileged. */
+ /* don't bmap a snapshot, since the mapping can change */
+ if (lv_ptr->lv_access & LV_SNAPSHOT)
+ return -EPERM;
return lvm_user_bmap(inode, (struct lv_bmap *) arg);

@@ -1075,8 +1101,8 @@
return -EFAULT;

memset(&bh,0,sizeof bh);
- bh.b_rsector = block;
- bh.b_dev = bh.b_rdev = inode->i_dev;
+ bh.b_blocknr = block;
+ bh.b_dev = bh.b_rdev = inode->i_rdev;
bh.b_size = lvm_get_blksize(bh.b_dev);
if ((err=lvm_map(&bh, READ)) < 0) {
printk("lvm map failed: %d\n", err);
@@ -1084,7 +1110,8 @@

return put_user(kdev_t_to_nr(bh.b_rdev), &user_result->lv_dev) ||
- put_user(bh.b_rsector, &user_result->lv_block) ? -EFAULT : 0;
+ put_user(bh.b_rsector/(bh.b_size>>9), &user_result->lv_block) ?
+ -EFAULT : 0;

diff -ru linux-2.4.6.orig/include/linux/lvm.h linux-2.4.6-aed/include/linux/lvm.h
--- linux-2.4.6.orig/include/linux/lvm.h Tue Apr 10 16:43:37 2001
+++ linux-2.4.6-aed/include/linux/lvm.h Thu Jun 28 15:52:52 2001
@@ -299,7 +314,7 @@

#define LVM_SNAPSHOT_MAX_CHUNK 1024 /* 1024 KB */
#define LVM_SNAPSHOT_DEF_CHUNK 64 /* 64 KB */
-#define LVM_SNAPSHOT_MIN_CHUNK 1 /* 1 KB */
+#define LVM_SNAPSHOT_MIN_CHUNK (PAGE_SIZE/1024) /* 4 or 8 KB */

#define UNDEF -1
#define FALSE 0
@@ -585,7 +585,7 @@
} le_remap_req_t;

typedef struct lv_bmap {
- ulong lv_block;
+ uint32_t lv_block;
dev_t lv_dev;
} lv_bmap_t;

Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto,
\ would they cancel out, leaving him still hungry?" -- Dogbert
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