contrib/elf2dmp: Ensure phdrs fit in file

Callers of elf64_getphdr() and elf_getphdrnum() assume phdrs are
accessible.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2202
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Tested-by: Viktor Prutyanov <viktor.prutyanov@phystech.edu>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20240307-elf2dmp-v4-19-4f324ad4d99d@daynix.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

contrib/elf2dmp/qemu_elf.c

@@ -132,6 +132,7 @@ static void exit_states(QEMU_Elf *qe)
 static bool check_ehdr(QEMU_Elf *qe)
 {
     Elf64_Ehdr *ehdr = qe->map;
+    uint64_t phendoff;
 
     if (sizeof(Elf64_Ehdr) > qe->size) {
         eprintf("Invalid input dump file size\n");
@@ -173,6 +174,13 @@ static bool check_ehdr(QEMU_Elf *qe)
         return false;
     }
 
+    if (umul64_overflow(ehdr->e_phnum, sizeof(Elf64_Phdr), &phendoff) ||
+        uadd64_overflow(phendoff, ehdr->e_phoff, &phendoff) ||
+        phendoff > qe->size) {
+        eprintf("phdrs do not fit in file\n");
+        return false;
+    }
+
     return true;
 }