If some metadata block, such as an allocation bitmap, overlaps the superblock, it's very likely that if the file system is mounted read/write, the results will not be pretty. So disallow r/w mounts for file systems corrupted in this particular way.

Signed-off-by: Theodore Ts'o tytso@mit.edu Cc: stable@vger.kernel.org --- fs/ext4/super.c | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 7cd022c344d1..edcfe6956eba 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -2335,6 +2335,8 @@ static int ext4_check_descriptors(struct super_block *sb, ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: " "Block bitmap for group %u overlaps " "superblock", i); + if (!sb_rdonly(sb)) + return 0; } if (block_bitmap < first_block || block_bitmap > last_block) { ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: " @@ -2347,6 +2349,8 @@ static int ext4_check_descriptors(struct super_block *sb, ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: " "Inode bitmap for group %u overlaps " "superblock", i); + if (!sb_rdonly(sb)) + return 0; } if (inode_bitmap < first_block || inode_bitmap > last_block) { ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: " @@ -2359,6 +2363,8 @@ static int ext4_check_descriptors(struct super_block *sb, ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: " "Inode table for group %u overlaps " "superblock", i); + if (!sb_rdonly(sb)) + return 0; } if (inode_table < first_block || inode_table + sbi->s_itb_per_group - 1 > last_block) {

On 26.03.2018 07:49, Theodore Ts'o wrote:

The extended attribute code now uses the crc32c checksum for hashing purposes, so we should just always always initialize it. We also want to prevent NULL pointer dereferences if one of the metadata checksum features is enabled after the file sytsem is originally mounted.

https://bugzilla.kernel.org/show_bug.cgi?id=199183

Signed-off-by: Theodore Ts'o tytso@mit.edu Cc: stable@vger.kernel.org

---

fs/ext4/super.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 9d1da40c1f62..7cd022c344d1 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -3492,15 +3492,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) } /* Load the checksum driver */

• if (ext4_has_feature_metadata_csum(sb) ||

•    ext4_has_feature_ea_inode(sb)) {
  

• sbi->s_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
  

• if (IS_ERR(sbi->s_chksum_driver)) {
  

• 	ext4_msg(sb, KERN_ERR, "Cannot load crc32c driver.");
  

• 	ret = PTR_ERR(sbi->s_chksum_driver);
  

• 	sbi->s_chksum_driver = NULL;
  

• 	goto failed_mount;
  

• }
  

• sbi->s_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
• if (IS_ERR(sbi->s_chksum_driver)) {

• ext4_msg(sb, KERN_ERR, "Cannot load crc32c driver.");
  

• ret = PTR_ERR(sbi->s_chksum_driver);
  

• sbi->s_chksum_driver = NULL;
  

• goto failed_mount;
  

  }

Why do you need to do all the manual initialization of the crc32c lowlevel driver, when you can just make ext4 select LIBCRC32c and in the code just use crc32c? Refer to include/linux/crc32c.h for the interface and lib/libcrc32c.c for the low-level details.

/* Check superblock checksum */