[PATCH v4] fs/fs_parse: Remove unused and problematic validate_constant_table()

[Zijun Hu]

From: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>

Remove validate_constant_table() since:

- It has no caller.

- It has below 3 bugs for good constant table array array[] which must
  end with a empty entry, and take below invocation for explaination:
  validate_constant_table(array, ARRAY_SIZE(array), ...)

  - Always return wrong value due to the last empty entry.
  - Imprecise error message for missorted case.
  - Potential NULL pointer dereference since the last pr_err() may use
    @tbl[i].name NULL pointer to print the last empty entry's name.

Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
---
Changes in v4:
- Rebase on vfs-6.16.misc branch to fix merge conflict.
- Link to v3: https://lore.kernel.org/r/20250415-fix_fs-v3-1-0c378cc5ce35@xxxxxxxxxxx

Changes in v3:
- Remove validate_constant_table() instead of fixing it
- Link to v2: https://lore.kernel.org/r/20250411-fix_fs-v2-2-5d3395c102e4@xxxxxxxxxxx

Changes in v2:
- Remove fixes tag for remaining patches
- Add more comment for the NULL pointer dereference issue
- Link to v1: https://lore.kernel.org/r/20250410-fix_fs-v1-3-7c14ccc8ebaa@xxxxxxxxxxx
---
 Documentation/filesystems/mount_api.rst | 15 ----------
 fs/fs_parser.c                          | 49 ---------------------------------
 include/linux/fs_parser.h               |  5 ----
 3 files changed, 69 deletions(-)

diff --git a/Documentation/filesystems/mount_api.rst b/Documentation/filesystems/mount_api.rst
index 47dafbb7427e6a829989a815e4d034e48fdbe7a2..e149b89118c885c377a17b95adcdbcb594b34e00 100644
--- a/Documentation/filesystems/mount_api.rst
+++ b/Documentation/filesystems/mount_api.rst
@@ -752,21 +752,6 @@ process the parameters it is given.
      If a match is found, the corresponding value is returned.  If a match
      isn't found, the not_found value is returned instead.
 
-   * ::
-
-       bool validate_constant_table(const struct constant_table *tbl,
-				    size_t tbl_size,
-				    int low, int high, int special);
-
-     Validate a constant table.  Checks that all the elements are appropriately
-     ordered, that there are no duplicates and that the values are between low
-     and high inclusive, though provision is made for one allowable special
-     value outside of that range.  If no special value is required, special
-     should just be set to lie inside the low-to-high range.
-
-     If all is good, true is returned.  If the table is invalid, errors are
-     logged to the kernel log buffer and false is returned.
-
    * ::
 
        bool fs_validate_description(const char *name,
diff --git a/fs/fs_parser.c b/fs/fs_parser.c
index c5cb19788f74771a945801ceedeec69efed0e40a..c092a9f79e324bacbd950165a0eb66632cae9e03 100644
--- a/fs/fs_parser.c
+++ b/fs/fs_parser.c
@@ -379,55 +379,6 @@ int fs_param_is_path(struct p_log *log, const struct fs_parameter_spec *p,
 EXPORT_SYMBOL(fs_param_is_path);
 
 #ifdef CONFIG_VALIDATE_FS_PARSER
-/**
- * validate_constant_table - Validate a constant table
- * @tbl: The constant table to validate.
- * @tbl_size: The size of the table.
- * @low: The lowest permissible value.
- * @high: The highest permissible value.
- * @special: One special permissible value outside of the range.
- */
-bool validate_constant_table(const struct constant_table *tbl, size_t tbl_size,
-			     int low, int high, int special)
-{
-	size_t i;
-	bool good = true;
-
-	if (tbl_size == 0) {
-		pr_warn("VALIDATE C-TBL: Empty\n");
-		return true;
-	}
-
-	for (i = 0; i < tbl_size; i++) {
-		if (!tbl[i].name) {
-			pr_err("VALIDATE C-TBL[%zu]: Null\n", i);
-			good = false;
-		} else if (i > 0 && tbl[i - 1].name) {
-			int c = strcmp(tbl[i-1].name, tbl[i].name);
-
-			if (c == 0) {
-				pr_err("VALIDATE C-TBL[%zu]: Duplicate %s\n",
-				       i, tbl[i].name);
-				good = false;
-			}
-			if (c > 0) {
-				pr_err("VALIDATE C-TBL[%zu]: Missorted %s>=%s\n",
-				       i, tbl[i-1].name, tbl[i].name);
-				good = false;
-			}
-		}
-
-		if (tbl[i].value != special &&
-		    (tbl[i].value < low || tbl[i].value > high)) {
-			pr_err("VALIDATE C-TBL[%zu]: %s->%d const out of range (%d-%d)\n",
-			       i, tbl[i].name, tbl[i].value, low, high);
-			good = false;
-		}
-	}
-
-	return good;
-}
-
 /**
  * fs_validate_description - Validate a parameter specification array
  * @name: Owner name of the parameter specification array
diff --git a/include/linux/fs_parser.h b/include/linux/fs_parser.h
index 5057faf4f09182fa6e7ddd03fb17b066efd7e58b..5a0e897cae807bbf5472645735027883a6593e91 100644
--- a/include/linux/fs_parser.h
+++ b/include/linux/fs_parser.h
@@ -87,14 +87,9 @@ extern int lookup_constant(const struct constant_table tbl[], const char *name,
 extern const struct constant_table bool_names[];
 
 #ifdef CONFIG_VALIDATE_FS_PARSER
-extern bool validate_constant_table(const struct constant_table *tbl, size_t tbl_size,
-				    int low, int high, int special);
 extern bool fs_validate_description(const char *name,
 				    const struct fs_parameter_spec *desc);
 #else
-static inline bool validate_constant_table(const struct constant_table *tbl, size_t tbl_size,
-					   int low, int high, int special)
-{ return true; }
 static inline bool fs_validate_description(const char *name,
 					   const struct fs_parameter_spec *desc)
 { return true; }

---
base-commit: 8cc42084abd926e3f005d7f5c23694c598b29cee
change-id: 20250410-fix_fs-6e0a97c4e59f

Best regards,
-- 
Zijun Hu <quic_zijuhu@xxxxxxxxxxx>