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fix(mqtt5): Fix UB in variable len processing

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This commit is contained in:
David Cermak
2025-12-30 15:49:16 +01:00
parent b6e8c65305
commit 3c5777d706
1 changed files with 10 additions and 2 deletions
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lib/mqtt5_msg.c
+10 -2
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@@ -61,8 +61,10 @@ static size_t get_variable_len(uint8_t *buffer, size_t offset, size_t buffer_len
*len_bytes = 0;
size_t len = 0, i = 0;
for (i = offset; i < buffer_length; i ++) {
len += (buffer[i] & 0x7f) << (7 * (i - offset));
// MQTT Variable Byte Integer is max 4 bytes (MQTT v5 spec).
// Limit decoding to 4 bytes to avoid undefined shift behavior on malformed inputs.
for (i = offset; i < buffer_length && (i - offset) < 4; i ++) {
len += ((size_t)(buffer[i] & 0x7f)) << (7 * (i - offset));
if ((buffer[i] & 0x80) == 0) {
i ++;
@@ -70,6 +72,12 @@ static size_t get_variable_len(uint8_t *buffer, size_t offset, size_t buffer_len
}
}
// If the varint didn't terminate within 4 bytes, treat as invalid (0 bytes consumed).
if ((i - offset) == 4 && i <= buffer_length && (buffer[i - 1] & 0x80)) {
*len_bytes = 0;
return 0;
}
*len_bytes = i - offset;
return len;
}