[PATCH v2 1/2] efi_loader: fix string table reallocations

["Vincent Stehlé" <vincent.stehle@arm.com>]

The new_string() and set_string() HII string protocol functions keep
using old pointers after calling realloc(), which may have moved.

The set_string() function also assumes that reallocation only grew the
array by one element when computing the start of the memory to clear,
and forgets to update nstrings to the new table size after reallocation.

Repair and factorize the reallocation code in a new grow_string_table()
function to fix those issues.

Fixes: c9bfb22296b0 ("efi_loader: Initial HII database protocols")
Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Tom Rini <trini@konsulko.com>
---
 lib/efi_loader/efi_hii.c | 64 +++++++++++++++++++++++++++---------------------
 1 file changed, 36 insertions(+), 28 deletions(-)

diff --git a/lib/efi_loader/efi_hii.c b/lib/efi_loader/efi_hii.c
index 7bf51ad43d1..90dff91e5d4 100644
--- a/lib/efi_loader/efi_hii.c
+++ b/lib/efi_loader/efi_hii.c
@@ -822,6 +822,37 @@ static bool language_match(char *language, char *languages)
 	return false;
 }
 
+/**
+ * grow_string_table() - Grow a string table if necessary.
+ * @stbl: String table to grow.
+ * @n:    Minimum table size desired.
+ *
+ * Make sure a string table can contain at least n elements.
+ * If the table is too small, reallocate the memory and clear the new elements.
+ *
+ * Return: false in case of reallocation error, true otherwise.
+ * In case of error, the original string table is left untouched.
+ * In case of success, stbl->strings and stbl->nstrings may have been updated.
+ */
+static bool grow_string_table(struct efi_string_table *stbl, u32 n)
+{
+	void *buf;
+	u32 old_n = stbl->nstrings;
+
+	if (old_n >= n)
+		return true;
+
+	buf = realloc(stbl->strings, sizeof(stbl->strings[0]) * n);
+	if (!buf)
+		return false;
+
+	stbl->strings = buf;
+	stbl->nstrings = n;
+	memset(&stbl->strings[old_n], 0, sizeof(stbl->strings[0]) * (n - old_n));
+
+	return true;
+}
+
 static efi_status_t EFIAPI
 new_string(const struct efi_hii_string_protocol *this,
 	   efi_hii_handle_t package_list,
@@ -847,23 +878,12 @@ new_string(const struct efi_hii_string_protocol *this,
 	list_for_each_entry(stbl, &hii->string_tables, link) {
 		if (language_match((char *)language, stbl->language)) {
 			efi_string_id_t new_id;
-			void *buf;
 			efi_string_t str;
 
 			new_id = ++hii->max_string_id;
-			if (stbl->nstrings < new_id) {
-				buf = realloc(stbl->strings,
-					      sizeof(stbl->strings[0])
-						* new_id);
-				if (!buf)
-					return EFI_EXIT(EFI_OUT_OF_RESOURCES);
-
-				memset(&stbl->strings[stbl->nstrings], 0,
-				       (new_id - stbl->nstrings)
-					 * sizeof(stbl->strings[0]));
-				stbl->strings = buf;
-				stbl->nstrings = new_id;
-			}
+
+			if (!grow_string_table(stbl, new_id))
+				return EFI_EXIT(EFI_OUT_OF_RESOURCES);
 
 			str = u16_strdup(string);
 			if (!str)
@@ -957,20 +977,8 @@ set_string(const struct efi_hii_string_protocol *this,
 			if (hii->max_string_id < string_id)
 				return EFI_EXIT(EFI_NOT_FOUND);
 
-			if (stbl->nstrings < string_id) {
-				void *buf;
-
-				buf = realloc(stbl->strings,
-					      string_id
-						* sizeof(stbl->strings[0]));
-				if (!buf)
-					return EFI_EXIT(EFI_OUT_OF_RESOURCES);
-
-				memset(&stbl->strings[string_id - 1], 0,
-				       (string_id - stbl->nstrings)
-					 * sizeof(stbl->strings[0]));
-				stbl->strings = buf;
-			}
+			if (!grow_string_table(stbl, string_id))
+				return EFI_EXIT(EFI_OUT_OF_RESOURCES);
 
 			str = u16_strdup(string);
 			if (!str)

-- 
2.53.0