tests: Set errno in FuzzedFileProvider. Implement seek(..., ..., SEEK_END).

src/test/fuzz/util.h

@@ -259,6 +259,16 @@ void SetFuzzedErrNo(FuzzedDataProvider& fuzzed_data_provider, const std::array<T
     errno = fuzzed_data_provider.PickValueInArray(errnos);
 }
 
+/*
+ * Sets a fuzzed errno in the range [0, 133 (EHWPOISON)]. Can be used from functions emulating
+ * standard library functions that set errno, or in other contexts where the value of errno
+ * might be relevant for the execution path that will be taken.
+ */
+inline void SetFuzzedErrNo(FuzzedDataProvider& fuzzed_data_provider) noexcept
+{
+    errno = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, 133);
+}
+
 /**
  * Returns a byte vector of specified size regardless of the number of remaining bytes available
  * from the fuzzer. Pads with zero value bytes if needed to achieve the specified size.
@@ -345,6 +355,7 @@ public:
 
     FILE* open()
     {
+        SetFuzzedErrNo(m_fuzzed_data_provider);
         if (m_fuzzed_data_provider.ConsumeBool()) {
             return nullptr;
         }
@@ -386,6 +397,7 @@ public:
     static ssize_t read(void* cookie, char* buf, size_t size)
     {
         FuzzedFileProvider* fuzzed_file = (FuzzedFileProvider*)cookie;
+        SetFuzzedErrNo(fuzzed_file->m_fuzzed_data_provider);
         if (buf == nullptr || size == 0 || fuzzed_file->m_fuzzed_data_provider.ConsumeBool()) {
             return fuzzed_file->m_fuzzed_data_provider.ConsumeBool() ? 0 : -1;
         }
@@ -404,6 +416,7 @@ public:
     static ssize_t write(void* cookie, const char* buf, size_t size)
     {
         FuzzedFileProvider* fuzzed_file = (FuzzedFileProvider*)cookie;
+        SetFuzzedErrNo(fuzzed_file->m_fuzzed_data_provider);
         const ssize_t n = fuzzed_file->m_fuzzed_data_provider.ConsumeIntegralInRange<ssize_t>(0, size);
         if (AdditionOverflow(fuzzed_file->m_offset, (int64_t)n)) {
             return fuzzed_file->m_fuzzed_data_provider.ConsumeBool() ? 0 : -1;
@@ -414,8 +427,9 @@ public:
 
     static int seek(void* cookie, int64_t* offset, int whence)
     {
-        assert(whence == SEEK_SET || whence == SEEK_CUR); // SEEK_END not implemented yet.
+        assert(whence == SEEK_SET || whence == SEEK_CUR || whence == SEEK_END);
         FuzzedFileProvider* fuzzed_file = (FuzzedFileProvider*)cookie;
+        SetFuzzedErrNo(fuzzed_file->m_fuzzed_data_provider);
         int64_t new_offset = 0;
         if (whence == SEEK_SET) {
             new_offset = *offset;
@@ -424,6 +438,12 @@ public:
                 return -1;
             }
             new_offset = fuzzed_file->m_offset + *offset;
+        } else if (whence == SEEK_END) {
+            const int64_t n = fuzzed_file->m_fuzzed_data_provider.ConsumeIntegralInRange<int64_t>(0, 4096);
+            if (AdditionOverflow(n, *offset)) {
+                return -1;
+            }
+            new_offset = n + *offset;
         }
         if (new_offset < 0) {
             return -1;
@@ -436,6 +456,7 @@ public:
     static int close(void* cookie)
     {
         FuzzedFileProvider* fuzzed_file = (FuzzedFileProvider*)cookie;
+        SetFuzzedErrNo(fuzzed_file->m_fuzzed_data_provider);
         return fuzzed_file->m_fuzzed_data_provider.ConsumeIntegralInRange<int>(-1, 0);
     }
 };