Dear Ted,
I'm sending an improved patch as I've come to the conclusion that the
previous patch is too lenient in two ways:
* off-by-one in the check of the upper block limit
* it shouldn't stop when encountering a reference to block number zero
because, if I'm not mistaken, references behind it still might be
accessed in sparse files / when seeking behind the end of a file.
On the other hand, I decided to drop the check against
s_first_data_block at the low end to improve performance, since the
purpose of the patch is to prevent access to blocks outside the
filesystem, and not to do the best-possible consistency check against
indirect blocks, which probably is better done in fsck.
Anyways, in case you would be interested in having more checks here (eg.
as a compile-time option), I have available a more sophisticated patch
which also checks for non-zero block references behind the end of the file.
Kind regards,
Signed-off-by: Thiemo Nagel <thiemo.nagel@xxxxxxxxx>
--- linux-2.6.29-rc7/fs/ext4/inode.c.orig 2009-03-20 11:35:45.000000000 +0100
+++ linux-2.6.29-rc7/fs/ext4/inode.c 2009-03-20 13:48:25.000000000 +0100
@@ -371,6 +371,34 @@
return n;
}
+static int __ext4_check_blockref(const char *function, struct inode *inode,
+ unsigned int *p, unsigned int max) {
+
+ unsigned int maxblocks = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es);
+ unsigned int *bref = p;
+ while (bref < p+max) {
+ if (unlikely(*bref >= maxblocks)) {
+ ext4_error(inode->i_sb, function,
+ "block reference %u >= max (%u) "
+ "in inode #%lu, offset=%u",
+ *bref, maxblocks,
+ inode->i_ino, bref-p);
+ return -EIO;
+ }
+ bref++;
+ }
+ return 0;
+}
+
+
+#define ext4_check_indirect_blockref(inode, bh) \
+ __ext4_check_blockref(__func__, inode, (__le32 *)(bh)->b_data, \
+ EXT4_ADDR_PER_BLOCK((inode)->i_sb))
+
+#define ext4_check_inode_blockref(inode) \
+ __ext4_check_blockref(__func__, inode, EXT4_I(inode)->i_data, \
+ EXT4_NDIR_BLOCKS)
+
/**
* ext4_get_branch - read the chain of indirect blocks leading to data
* @inode: inode in question
@@ -418,6 +446,9 @@
bh = sb_bread(sb, le32_to_cpu(p->key));
if (!bh)
goto failure;
+ if (ext4_check_indirect_blockref(inode, bh))
+ goto failure;
+
add_chain(++p, bh, (__le32 *)bh->b_data + *++offsets);
/* Reader: end */
if (!p->key)
@@ -4302,11 +4333,13 @@
if (ei->i_flags & EXT4_EXTENTS_FL) {
/* Validate extent which is part of inode */
ret = ext4_ext_check_inode(inode);
- if (ret) {
- brelse(bh);
- goto bad_inode;
- }
-
+ } else {
+ /* Validate block references which are part of inode */
+ ret = ext4_check_inode_blockref(inode);
+ }
+ if (ret) {
+ brelse(bh);
+ goto bad_inode;
}
if (S_ISREG(inode->i_mode)) {
