From 4ec110281379826c5cf6ed14735e47027c3c5765 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Tue, 6 Jan 2009 14:53:26 -0500 Subject: [PATCH] ext4: Add sanity checks for the superblock before mounting the filesystem This avoids insane superblock configurations that could lead to kernel oops due to null pointer derefences. http://bugzilla.kernel.org/show_bug.cgi?id=12371 Thanks to David Maciejak at Fortinet's FortiGuard Global Security Research Team who discovered this bug independently (but at approximately the same time) as Thiemo Nagel, who submitted the patch. Signed-off-by: Thiemo Nagel Signed-off-by: "Theodore Ts'o" Cc: stable@kernel.org --- fs/ext4/super.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 8ff8709828fd..517c90ad25bd 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -2041,8 +2041,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) const char *descr; int ret = -EINVAL; int blocksize; - int db_count; - int i; + unsigned int db_count; + unsigned int i; int needs_recovery, has_huge_files; int features; __u64 blocks_count; @@ -2331,20 +2331,30 @@ 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)); + /* + * It makes no sense for the first data block to be beyond the end + * of the filesystem. + */ + if (le32_to_cpu(es->s_first_data_block) >= ext4_blocks_count(es)) { + printk(KERN_WARNING "EXT4-fs: bad geometry: first data" + "block %u is beyond end of filesystem (%llu)\n", + le32_to_cpu(es->s_first_data_block), + ext4_blocks_count(es)); goto failed_mount; } blocks_count = (ext4_blocks_count(es) - le32_to_cpu(es->s_first_data_block) + EXT4_BLOCKS_PER_GROUP(sb) - 1); do_div(blocks_count, EXT4_BLOCKS_PER_GROUP(sb)); + if (blocks_count > ((uint64_t)1<<32) - EXT4_DESC_PER_BLOCK(sb)) { + printk(KERN_WARNING "EXT4-fs: groups count too large: %u " + "(block count %llu, first data block %u, " + "blocks per group %lu)\n", sbi->s_groups_count, + ext4_blocks_count(es), + le32_to_cpu(es->s_first_data_block), + EXT4_BLOCKS_PER_GROUP(sb)); + goto failed_mount; + } sbi->s_groups_count = blocks_count; db_count = (sbi->s_groups_count + EXT4_DESC_PER_BLOCK(sb) - 1) / EXT4_DESC_PER_BLOCK(sb); -- 2.39.5