[PATCH 5/7] lib/glob: add glob_validate() for pattern syntax checking

Josh Law
2026-03-15T17:11:14Z

Add glob_validate() which checks whether a glob pattern is
syntactically well-formed before matching. It detects:

- Unclosed character classes: a '[' with no matching ']'
- Trailing backslash: a '\' at end of pattern with nothing to escape

glob_match() already handles these gracefully (unclosed brackets are
matched literally, a trailing backslash matches itself), but callers
like ftrace filters or sysfs attribute stores that accept patterns
from userspace may want to reject malformed input upfront with a
clear error rather than silently falling back to literal matching.

Signed-off-by: Josh Law <objecting@objecting.org>
---
include/linux/glob.h | 1 +
lib/glob.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)

diff --git a/include/linux/glob.h b/include/linux/glob.h
index 36527ae89730..deceaa2e4a74 100644
--- a/include/linux/glob.h
+++ b/include/linux/glob.h
@@ -7,5 +7,6 @@

bool __pure glob_match(char const *pat, char const *str);
bool __pure glob_match_nocase(char const *pat, char const *str);
+bool __pure glob_validate(char const *pat);

#endif /* _LINUX_GLOB_H */
diff --git a/lib/glob.c b/lib/glob.c
index 9c71ccc15abc..800163ed4dbf 100644
--- a/lib/glob.c
+++ b/lib/glob.c
@@ -186,3 +186,47 @@ bool __pure glob_match_nocase(char const *pat, char const *str)
return __glob_match(pat, str, true);
}
EXPORT_SYMBOL(glob_match_nocase);
+
+/**
+ * glob_validate - Check whether a glob pattern is well-formed
+ * @pat: Shell-style pattern to validate.
+ *
+ * Return: true if @pat is a syntactically valid glob pattern, false
+ * if it contains malformed constructs. The following are considered
+ * invalid:
+ *
+ * - An opening '[' with no matching ']' (unclosed character class).
+ * - A trailing '\' with no character following it.
+ *
+ * Note that glob_match() handles these gracefully (an unclosed bracket
+ * is matched literally, a trailing backslash matches itself), but
+ * callers that accept patterns from user input may wish to reject
+ * malformed patterns early with a clear error.
+ */
+bool __pure glob_validate(char const *pat)
+{
+ while (*pat) {
+ switch (*pat++) {
+ case '\\':
+ if (*pat == '\0')
+ return false;
+ pat++;
+ break;
+ case '[': {
+ if (*pat == '!' || *pat == '^')
+ pat++;
+ /* ] as first character is literal, not end of class */
+ if (*pat == ']')
+ pat++;
+ while (*pat && *pat != ']')
+ pat++;
+ if (*pat == '\0')
+ return false;
+ pat++; /* skip ']' */
+ break;
+ }
+ }
+ }
+ return true;
+}
+EXPORT_SYMBOL(glob_validate);
--
2.34.1