encoding-guesser: Avoid reading uninitialized data for zero-length files.

Found while investigating bug #61254.
Thanks to Irfan Ariq for reporting this bug.

diff --git a/src/libpspp/encoding-guesser.c b/src/libpspp/encoding-guesser.c
index 9518bd6396bd7d05472251e3ea779021dd459084..2f3438ff811ad954359261686871cd061db7bc48 100644 (file)
--- a/src/libpspp/encoding-guesser.c
+++ b/src/libpspp/encoding-guesser.c
@@ -189,28 +189,34 @@ is_utf8_bom (const uint8_t *data, size_t n)
   return n >= 3 && data[0] == 0xef && data[1] == 0xbb && data[2] == 0xbf;
 }
 
+static bool
+is_bom_length (size_t n, size_t w)
+{
+  return n >= ENCODING_GUESS_MIN || (n && n % w == 0);
+}
+
 static bool
 is_utf16le_bom (const uint8_t *data, size_t n)
 {
-  return (n >= ENCODING_GUESS_MIN || n % 2 == 0) && get_le16 (data) == 0xfeff;
+  return is_bom_length (n, 2) && get_le16 (data) == 0xfeff;
 }
 
 static bool
 is_utf16be_bom (const uint8_t *data, size_t n)
 {
-  return (n >= ENCODING_GUESS_MIN || n % 2 == 0) && get_be16 (data) == 0xfeff;
+  return is_bom_length (n, 2) && get_be16 (data) == 0xfeff;
 }
 
 static bool
 is_utf32le_bom (const uint8_t *data, size_t n)
 {
-  return (n >= ENCODING_GUESS_MIN || n % 4 == 0) && get_le32 (data) == 0xfeff;
+  return is_bom_length (n, 4) && get_le32 (data) == 0xfeff;
 }
 
 static bool
 is_utf32be_bom (const uint8_t *data, size_t n)
 {
-  return (n >= ENCODING_GUESS_MIN || n % 4 == 0) && get_be32 (data) == 0xfeff;
+  return is_bom_length (n, 4) && get_be32 (data) == 0xfeff;
 }
 
 /* Attempts to guess the encoding of a text file based on ENCODING, an encoding