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generic_ci_d_compare(): use shortname_storage

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... and check the "name might be unstable" predicate
the right way.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Gabriel Krisman Bertazi <gabriel@krisman.be>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2024-12-23 02:23:00 -05:00
parent 7e3270165a
commit 4c43ab1b10
1 changed files with 8 additions and 7 deletions
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15
fs/libfs.c
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@@ -1789,7 +1789,7 @@ int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
{
const struct dentry *parent;
const struct inode *dir;
char strbuf[DNAME_INLINE_LEN];
union shortname_store strbuf;
struct qstr qstr;
/*
@@ -1809,22 +1809,23 @@ int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
if (!dir || !IS_CASEFOLDED(dir))
return 1;
qstr.len = len;
qstr.name = str;
/*
* If the dentry name is stored in-line, then it may be concurrently
* modified by a rename. If this happens, the VFS will eventually retry
* the lookup, so it doesn't matter what ->d_compare() returns.
* However, it's unsafe to call utf8_strncasecmp() with an unstable
* string. Therefore, we have to copy the name into a temporary buffer.
* As above, len is guaranteed to match str, so the shortname case
* is exactly when str points to ->d_shortname.
*/
if (len <= DNAME_INLINE_LEN - 1) {
memcpy(strbuf, str, len);
strbuf[len] = 0;
str = strbuf;
if (qstr.name == dentry->d_shortname.string) {
strbuf = dentry->d_shortname; // NUL is guaranteed to be in there
qstr.name = strbuf.string;
/* prevent compiler from optimizing out the temporary buffer */
barrier();
}
qstr.len = len;
qstr.name = str;
return utf8_strncasecmp(dentry->d_sb->s_encoding, name, &qstr);
}