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ext4: introduce linear search for dentries

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This patch addresses an issue where some files in case-insensitive
directories become inaccessible due to changes in how the kernel
function, utf8_casefold(), generates case-folded strings from the
commit 5c26d2f1d3 ("unicode: Don't special case ignorable code
points").

There are good reasons why this change should be made; it's actually
quite stupid that Unicode seems to think that the characters ❤ and ❤️
should be casefolded.  Unfortimately because of the backwards
compatibility issue, this commit was reverted in 231825b2e1.

This problem is addressed by instituting a brute-force linear fallback
if a lookup fails on case-folded directory, which does result in a
performance hit when looking up files affected by the changing how
thekernel treats ignorable Uniode characters, or when attempting to
look up non-existent file names.  So this fallback can be disabled by
setting an encoding flag if in the future, the system administrator or
the manufacturer of a mobile handset or tablet can be sure that there
was no opportunity for a kernel to insert file names with incompatible
encodings.

Fixes: 5c26d2f1d3 ("unicode: Don't special case ignorable code points")
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
This commit is contained in:
Theodore Ts'o 2025-02-07 23:08:02 -05:00
parent a399af4e3b
commit 9e28059d56
2 changed files with 19 additions and 5 deletions
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14
fs/ext4/namei.c
View File

@ -1462,7 +1462,8 @@ static bool ext4_match(struct inode *parent,
* sure cf_name was properly initialized before
* considering the calculated hash.
*/
if (IS_ENCRYPTED(parent) && fname->cf_name.name &&
if (sb_no_casefold_compat_fallback(parent->i_sb) &&
IS_ENCRYPTED(parent) && fname->cf_name.name &&
(fname->hinfo.hash != EXT4_DIRENT_HASH(de) ||
fname->hinfo.minor_hash != EXT4_DIRENT_MINOR_HASH(de)))
return false;
@ -1595,10 +1596,15 @@ static struct buffer_head *__ext4_find_entry(struct inode *dir,
* return. Otherwise, fall back to doing a search the
* old fashioned way.
*/
if (!IS_ERR(ret) || PTR_ERR(ret) != ERR_BAD_DX_DIR)
if (IS_ERR(ret) && PTR_ERR(ret) == ERR_BAD_DX_DIR)
dxtrace(printk(KERN_DEBUG "ext4_find_entry: dx failed, "
"falling back\n"));
else if (!sb_no_casefold_compat_fallback(dir->i_sb) &&
*res_dir == NULL && IS_CASEFOLDED(dir))
dxtrace(printk(KERN_DEBUG "ext4_find_entry: casefold "
"failed, falling back\n"));
else
goto cleanup_and_exit;
dxtrace(printk(KERN_DEBUG "ext4_find_entry: dx failed, "
"falling back\n"));
ret = NULL;
}
nblocks = dir->i_size >> EXT4_BLOCK_SIZE_BITS(sb);

10
include/linux/fs.h
View File

@ -1258,11 +1258,19 @@ extern int send_sigurg(struct file *file);
#define SB_NOUSER BIT(31)
/* These flags relate to encoding and casefolding */
#define SB_ENC_STRICT_MODE_FL (1 << 0)
#define SB_ENC_STRICT_MODE_FL (1 << 0)
#define SB_ENC_NO_COMPAT_FALLBACK_FL (1 << 1)
#define sb_has_strict_encoding(sb) \
(sb->s_encoding_flags & SB_ENC_STRICT_MODE_FL)
#if IS_ENABLED(CONFIG_UNICODE)
#define sb_no_casefold_compat_fallback(sb) \
(sb->s_encoding_flags & SB_ENC_NO_COMPAT_FALLBACK_FL)
#else
#define sb_no_casefold_compat_fallback(sb) (1)
#endif
/*
* Umount options
*/