fix: remove a potential overflow before conversion (#1062)

* fix: remove a potential overflow before conversion

This is in response to CodeQL security scan alert #1-#3.

`Elf[32|64]_Ehdr[.e_phnum|.e_phentsize|.e_shnum|.e_shentsize]` are all `uint16_t`, this means the loop-var `i` is bounded by `uint16_t` and should fit in a `uint32_t` (to prevent unsigned overflow in the loop). A switch to unsigned still makes sense, because we reduce the future chance of unnecessary signed overflow (=UB) in the loop body.

All program/section-header table entry sizes are cast to `uin64_t` even though the multiplication is bound to `uint32_t` by both factors being bound by `uint16_t`. This fixes the potential overflow before conversion to the bigger type.

* also safely cast the access to section header string table.

Author: supervacuus

src/modulefinder/sentry_modulefinder_linux.c

@@ -303,10 +303,11 @@ get_code_id_from_program_header(const sentry_module_t *module, size_t *size_out)
         Elf64_Ehdr elf;
         ENSURE(sentry__module_read_safely(&elf, module, 0, sizeof(Elf64_Ehdr)));
 
-        for (int i = 0; i < elf.e_phnum; i++) {
+        for (uint32_t i = 0; i < elf.e_phnum; i++) {
             Elf64_Phdr header;
             ENSURE(sentry__module_read_safely(&header, module,
-                elf.e_phoff + elf.e_phentsize * i, sizeof(Elf64_Phdr)));
+                elf.e_phoff + (uint64_t)elf.e_phentsize * i,
+                sizeof(Elf64_Phdr)));
 
             // we are only interested in notes
             if (header.p_type != PT_NOTE) {
@@ -326,10 +327,11 @@ get_code_id_from_program_header(const sentry_module_t *module, size_t *size_out)
         Elf32_Ehdr elf;
         ENSURE(sentry__module_read_safely(&elf, module, 0, sizeof(Elf32_Ehdr)));
 
-        for (int i = 0; i < elf.e_phnum; i++) {
+        for (uint32_t i = 0; i < elf.e_phnum; i++) {
             Elf32_Phdr header;
             ENSURE(sentry__module_read_safely(&header, module,
-                elf.e_phoff + elf.e_phentsize * i, sizeof(Elf32_Phdr)));
+                elf.e_phoff + (uint64_t)elf.e_phentsize * i,
+                sizeof(Elf32_Phdr)));
 
             // we are only interested in notes
             if (header.p_type != PT_NOTE) {
@@ -360,13 +362,14 @@ get_code_id_from_program_header(const sentry_module_t *module, size_t *size_out)
                                                                                \
         Elf64_Shdr strheader;                                                  \
         ENSURE(sentry__module_read_safely(&strheader, module,                  \
-            elf.e_shoff + elf.e_shentsize * elf.e_shstrndx,                    \
+            elf.e_shoff + (uint64_t)elf.e_shentsize * elf.e_shstrndx,          \
             sizeof(Elf64_Shdr)));                                              \
                                                                                \
-        for (int i = 0; i < elf.e_shnum; i++) {                                \
+        for (uint32_t i = 0; i < elf.e_shnum; i++) {                           \
             Elf64_Shdr header;                                                 \
             ENSURE(sentry__module_read_safely(&header, module,                 \
-                elf.e_shoff + elf.e_shentsize * i, sizeof(Elf64_Shdr)));       \
+                elf.e_shoff + (uint64_t)elf.e_shentsize * i,                   \
+                sizeof(Elf64_Shdr)));                                          \
                                                                                \
             char name[6];                                                      \
             ENSURE(sentry__module_read_safely(name, module,                    \
@@ -382,13 +385,14 @@ get_code_id_from_program_header(const sentry_module_t *module, size_t *size_out)
                                                                                \
         Elf32_Shdr strheader;                                                  \
         ENSURE(sentry__module_read_safely(&strheader, module,                  \
-            elf.e_shoff + elf.e_shentsize * elf.e_shstrndx,                    \
+            elf.e_shoff + (uint64_t)elf.e_shentsize * elf.e_shstrndx,          \
             sizeof(Elf32_Shdr)));                                              \
                                                                                \
-        for (int i = 0; i < elf.e_shnum; i++) {                                \
+        for (uint32_t i = 0; i < elf.e_shnum; i++) {                           \
             Elf32_Shdr header;                                                 \
             ENSURE(sentry__module_read_safely(&header, module,                 \
-                elf.e_shoff + elf.e_shentsize * i, sizeof(Elf32_Shdr)));       \
+                elf.e_shoff + (uint64_t)elf.e_shentsize * i,                   \
+                sizeof(Elf32_Shdr)));                                          \
                                                                                \
             char name[6];                                                      \
             ENSURE(sentry__module_read_safely(name, module,                    \