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authorEric Sandeen <sandeen@redhat.com>2008-01-28 23:58:27 -0500
committerTheodore Ts'o <tytso@mit.edu>2008-01-28 23:58:27 -0500
commite7c95593001cb96ef5dd121a4523286c574c7133 (patch)
treee49d172341611a20e9e5394379801d4e97977a0b
parent07620f69eff6671fea6bd382c95709f757e33768 (diff)
ext4: fix oops on corrupted ext4 mount
When mounting an ext4 filesystem with corrupted s_first_data_block, things can go very wrong and oops. Because blocks_count in ext4_fill_super is a u64, and we must use do_div, the calculation of db_count is done differently than on ext4. If first_data_block is corrupted such that it is larger than ext4_blocks_count, for example, then the intermediate blocks_count value may go negative, but sign-extend to a very large value: blocks_count = (ext4_blocks_count(es) - le32_to_cpu(es->s_first_data_block) + EXT4_BLOCKS_PER_GROUP(sb) - 1); This is then assigned to s_groups_count which is an unsigned long: sbi->s_groups_count = blocks_count; This may result in a value of 0xFFFFFFFF which is then used to compute db_count: db_count = (sbi->s_groups_count + EXT4_DESC_PER_BLOCK(sb) - 1) / EXT4_DESC_PER_BLOCK(sb); and in this case db_count will wind up as 0 because the addition overflows 32 bits. This in turn causes the kmalloc for group_desc to be of 0 size: sbi->s_group_desc = kmalloc(db_count * sizeof (struct buffer_head *), GFP_KERNEL); and eventually in ext4_check_descriptors, dereferencing sbi->s_group_desc[desc_block] will result in a NULL pointer dereference. The simplest test seems to be to sanity check s_first_data_block, EXT4_BLOCKS_PER_GROUP, and ext4_blocks_count values to be sure their combination won't result in a bad intermediate value for blocks_count. We could just check for db_count == 0, but catching it at the root cause seems like it provides more info. Signed-off-by: Eric Sandeen <sandeen@redhat.com> Reviewed-by: Mingming Cao <cmm@us.ibm.com>
-rw-r--r--fs/ext4/super.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 1484a087bba..32e3ecb35cd 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1997,6 +1997,17 @@ static int ext4_fill_super (struct super_block *sb, void *data, int silent)
if (EXT4_BLOCKS_PER_GROUP(sb) == 0)
goto cantfind_ext4;
+
+ /* ensure blocks_count calculation below doesn't sign-extend */
+ if (ext4_blocks_count(es) + EXT4_BLOCKS_PER_GROUP(sb) <
+ le32_to_cpu(es->s_first_data_block) + 1) {
+ printk(KERN_WARNING "EXT4-fs: bad geometry: block count %llu, "
+ "first data block %u, blocks per group %lu\n",
+ ext4_blocks_count(es),
+ le32_to_cpu(es->s_first_data_block),
+ EXT4_BLOCKS_PER_GROUP(sb));
+ goto failed_mount;
+ }
blocks_count = (ext4_blocks_count(es) -
le32_to_cpu(es->s_first_data_block) +
EXT4_BLOCKS_PER_GROUP(sb) - 1);