libdwfl: Don't try to convert too many bytes in dwfl_link_map_report

When trying to read (corrupt) phdrs from a core file we only want
to read and convert the bytes we could read. Also make sure we don't
try to allocate too big buffers.

https://sourceware.org/bugzilla/show_bug.cgi?id=28666

Signed-off-by: Mark Wielaard <mark@klomp.org>

2 files changed, 21 insertions, 2 deletions

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index b2a8752a..96251f0d 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,5 +1,11 @@
 2021-12-08  Mark Wielaard  <mark@klomp.org>
 
+        * link_map.c (dwfl_link_map_report): Limit malloc size to max
+        possible. When converting make sure we don't exceed the number
+        of bytes available in either in.d_buf nor out.d_buf.
+
+2021-12-08  Mark Wielaard  <mark@klomp.org>
+
         * dwfl_segment_report_module.c (dwfl_segment_report_module): Don't
         read beyond of (actual) end of (memory) file.
 
diff --git a/libdwfl/link_map.c b/libdwfl/link_map.c
index 1e7d4502..1c298a8e 100644
--- a/libdwfl/link_map.c
+++ b/libdwfl/link_map.c
@@ -847,6 +847,11 @@ dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
               /* Note this in the !in_ok path.  That means memory_callback
                  failed.  But the callback might still have reset the d_size
                  value (to zero).  So explicitly set it here again.  */
+              if (unlikely (phnum > SIZE_MAX / phent))
+                {
+                  __libdwfl_seterrno (DWFL_E_NOMEM);
+                  return false;
+                }
               in.d_size = phnum * phent;
               in.d_buf = malloc (in.d_size);
               if (unlikely (in.d_buf == NULL))
@@ -876,6 +881,13 @@ dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
                   return false;
                 }
               size_t nbytes = phnum * phent;
+              /* We can only process as many bytes/phnum as there are
+                 in in.d_size. The data might have been truncated.  */
+              if (nbytes > in.d_size)
+                {
+                  nbytes = in.d_size;
+                  phnum = nbytes / phent;
+                }
               void *buf = malloc (nbytes);
               Elf32_Phdr (*p32)[phnum] = buf;
               Elf64_Phdr (*p64)[phnum] = buf;
@@ -888,10 +900,11 @@ dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
                 {
                   .d_type = ELF_T_PHDR,
                   .d_version = EV_CURRENT,
-                  .d_size = phnum * phent,
+                  .d_size = nbytes,
                   .d_buf = buf
                 };
-              in.d_size = out.d_size;
+              if (in.d_size > out.d_size)
+                in.d_size = out.d_size;
               if (likely ((elfclass == ELFCLASS32
                            ? elf32_xlatetom : elf64_xlatetom)
                           (&out, &in, elfdata) != NULL))