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Subject[PATCH]Fix potential Divide by Zero error in ext2_get_inode()

Found a line of code in ext2_get_inode function of inode.c in the ext2
filesystem that has the potential of hitting the divide by 0 error.
*************************************************
block_group = (ino - 1) / EXT2_INODES_PER_GROUP(sb);
*************************************************
There is no checking done here to verify if EXT2_INODES_PER_GROUP()
returns 0. This could result in divide by zero error and panic the system.
Below is the patch, built against 2.6.30-rc5, to correct the same:
Signed-off-by: B N Poornima <poornima@in.ibm.com>

Index: linux-2.6.30-rc5/fs/ext2/inode.c
===================================================================
--- linux-2.6.30-rc5.orig/fs/ext2/inode.c 2009-05-09
05:44:14.000000000 +0530
+++ linux-2.6.30-rc5/fs/ext2/inode.c 2009-05-12 19:14:42.873991280 +0530
@@ -1138,6 +1138,7 @@
unsigned long block_group;
unsigned long block;
unsigned long offset;
+ unsigned long inodes_per_group;
struct ext2_group_desc * gdp;

*p = NULL;
@@ -1145,7 +1146,10 @@
ino > le32_to_cpu(EXT2_SB(sb)->s_es->s_inodes_count))
goto Einval;

- block_group = (ino - 1) / EXT2_INODES_PER_GROUP(sb);
+ inodes_per_group = EXT2_INODES_PER_GROUP(sb);
+ if (!inodes_per_group)
+ goto Einval1;
+ block_group = (ino - 1) / inodes_per_group;
gdp = ext2_get_group_desc(sb, block_group, NULL);
if (!gdp)
goto Egdp;
@@ -1166,6 +1170,11 @@
ext2_error(sb, "ext2_get_inode", "bad inode number: %lu",
(unsigned long) ino);
return ERR_PTR(-EINVAL);
+
+Einval1:
+ printk(KERN_ERR "Ext2-fs: Filesystem corrupted. Wrong inodes per
group: %lu, run e2fsck\n", (unsigned long)inodes_per_group);
+ return ERR_PTR(-EINVAL);
+
Eio:
ext2_error(sb, "ext2_get_inode",
"unable to read inode block - inode=%lu, block=%lu",







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