[PULL 55/56] hw/elf_ops: defend against weird elf headers

From: Alex Bennée <[email protected]>

According to the ELF spec:

  PT_LOAD

  The array element specifies a loadable segment, described by
  p_filesz and p_memsz. The bytes from the file are mapped to the
  beginning of the memory segment. If the segment's memory
  size (p_memsz) is larger than the file size (p_filesz), the
  ``extra'' bytes are defined to hold the value 0 and to follow the
  segment's initialized area. The file size may not be larger than the
  memory size. Loadable segment entries in the program header table
  appear in ascending order, sorted on the p_vaddr member.

which implies while both p_filesz and p_memsz can be zero we should
never see a case where p_filesz is greater than the in memory size.
Indeed it has been reported such a hand crafted ELF can blow up, for
example during rom_reset():

  address_space_set(rom->as, rom->addr + rom->datasize, 0,
                    rom->romsize - rom->datasize,
                    MEMTXATTRS_UNSPECIFIED);

which could trigger and underflow leaving QEMU slowly filling a very
large buffer.

Cc: [email protected]
Fixes: https://gitlab.com/qemu-project/qemu/-/work_items/4056
Signed-off-by: Alex Bennée <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
---
 include/hw/elf_ops.h.inc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/hw/elf_ops.h.inc b/include/hw/elf_ops.h.inc
index 9c35d1b9da6..044e72de2a2 100644
--- a/include/hw/elf_ops.h.inc
+++ b/include/hw/elf_ops.h.inc
@@ -427,6 +427,11 @@ static ssize_t glue(load_elf, SZ)(const char *name, int fd,
             file_size = ph->p_filesz; /* Size of the allocated data */
             data_offset = ph->p_offset; /* Offset where the data is located */
 
+            if (file_size > mem_size) {
+                ret = ELF_LOAD_TOO_BIG;
+                goto fail;
+            }
+
             if (file_size > 0) {
                 if (g_mapped_file_get_length(mapped_file) <
                     file_size + data_offset) {
-- 
2.53.0