[gdb] Fix heap-buffer-overflow in find_program_interpreter

With the test-case included in this patch, we run into:
...
(gdb) target remote localhost:2347^M
`target:twice-connect' has disappeared; keeping its symbols.^M
Remote debugging using localhost:2347^M
warning: Unable to find dynamic linker breakpoint function.^M
GDB will be unable to debug shared library initializers^M
and track explicitly loaded dynamic code.^M
Reading /usr/lib/debug/.build-id/$hex/$hex.debug from remote target...^M
0x00007ffff7dd4550 in ?? ()^M
(gdb) PASS: gdb.server/twice-connect.exp: session=second: gdbserver started
FAIL: gdb.server/twice-connect.exp: found interpreter
...

The problem originates in find_program_interpreter, where
bfd_get_section_contents is called to read .interp, but fails.  The function
returns false but the result is ignored, so find_program_interpreter returns
some random string.

Fix this by checking the result of the call to bfd_get_section_contents.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29652

1 files changed, 5 insertions, 3 deletions

diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index 27267e0..7e83819 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -568,9 +568,11 @@ find_program_interpreter (void)
 	int sect_size = bfd_section_size (interp_sect);
 
 	gdb::byte_vector buf (sect_size);
-	bfd_get_section_contents (current_program_space->exec_bfd (),
-				  interp_sect, buf.data (), 0, sect_size);
-	return buf;
+	bool res
+	  = bfd_get_section_contents (current_program_space->exec_bfd (),
+				      interp_sect, buf.data (), 0, sect_size);
+	if (res)
+	  return buf;
       }
    }