From a9c0ae2863875446fa3d00edae2ccad4da75feb5 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Thu, 19 Jan 2023 09:50:38 -0800 Subject: [PATCH] ext4: deal with legacy signed xattr name hash values We potentially have old hashes of the xattr names generated on systems with signed 'char' types. Now that everybody uses '-funsigned-char', those hashes will no longer match. This only happens if you use xattrs names that have the high bit set, which probably doesn't happen in practice, but the xfstest generic/454 shows it. Instead of adding a new "signed xattr hash filesystem" bit and having to deal with all the possible combinations, just calculate the hash both ways if the first one fails, and always generate new hashes with the proper unsigned char version. Reported-by: kernel test robot Link: https://lore.kernel.org/oe-lkp/202212291509.704a11c9-oliver.sang@intel.com Link: https://lore.kernel.org/all/CAHk-=whUNjwqZXa-MH9KMmc_CpQpoFKFjAB9ZKHuu=TbsouT4A@mail.gmail.com/ Exposed-by: 3bc753c06dd0 ("kbuild: treat char as always unsigned") Cc: Eric Biggers Cc: Andreas Dilger Cc: Theodore Ts'o , Cc: Jason Donenfeld Cc: Masahiro Yamada Signed-off-by: Linus Torvalds --- fs/ext4/xattr.c | 41 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 39 insertions(+), 2 deletions(-) diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 7decaaf27e82..69a1b8c6a2ec 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -81,6 +81,8 @@ ext4_xattr_block_cache_find(struct inode *, struct ext4_xattr_header *, struct mb_cache_entry **); static __le32 ext4_xattr_hash_entry(char *name, size_t name_len, __le32 *value, size_t value_count); +static __le32 ext4_xattr_hash_entry_signed(char *name, size_t name_len, __le32 *value, + size_t value_count); static void ext4_xattr_rehash(struct ext4_xattr_header *); static const struct xattr_handler * const ext4_xattr_handler_map[] = { @@ -470,8 +472,21 @@ ext4_xattr_inode_verify_hashes(struct inode *ea_inode, tmp_data = cpu_to_le32(hash); e_hash = ext4_xattr_hash_entry(entry->e_name, entry->e_name_len, &tmp_data, 1); - if (e_hash != entry->e_hash) - return -EFSCORRUPTED; + /* All good? */ + if (e_hash == entry->e_hash) + return 0; + + /* + * Not good. Maybe the entry hash was calculated + * using the buggy signed char version? + */ + e_hash = ext4_xattr_hash_entry_signed(entry->e_name, entry->e_name_len, + &tmp_data, 1); + if (e_hash == entry->e_hash) + return 0; + + /* Still no match - bad */ + return -EFSCORRUPTED; } return 0; } @@ -3091,6 +3106,28 @@ static __le32 ext4_xattr_hash_entry(char *name, size_t name_len, __le32 *value, return cpu_to_le32(hash); } +/* + * ext4_xattr_hash_entry_signed() + * + * Compute the hash of an extended attribute incorrectly. + */ +static __le32 ext4_xattr_hash_entry_signed(char *name, size_t name_len, __le32 *value, size_t value_count) +{ + __u32 hash = 0; + + while (name_len--) { + hash = (hash << NAME_HASH_SHIFT) ^ + (hash >> (8*sizeof(hash) - NAME_HASH_SHIFT)) ^ + (signed char)*name++; + } + while (value_count--) { + hash = (hash << VALUE_HASH_SHIFT) ^ + (hash >> (8*sizeof(hash) - VALUE_HASH_SHIFT)) ^ + le32_to_cpu(*value++); + } + return cpu_to_le32(hash); +} + #undef NAME_HASH_SHIFT #undef VALUE_HASH_SHIFT -- 2.39.0.rc2.4.g1435931e43