[PATCH] fs/binfmt_elf.c:load_elf_binary() doesn't verify interpreter arch

From: Peter Bergner <bergner@vnet.ibm.com>

In fs/binfmt_elf.c:load_elf_binary() (both 2.6 and 2.4), there is some
minimal checking whether the interpreter it's about to load/run is a valid
ELF file, but it fails to check whether the interpreter is of the correct
arch.  We ran into this when a borked powerpc64-linux toolchain set the
interpreter on our 64-bit app to our 32-bit ld.so.  Executing the app
caused the kernel to really chew up memory.  I'm assuming x86_64 and
sparc64 might possibly see the same behavior.

Note I'm not sure of the history behind INTERPRETER_AOUT, so I added the
test for INTERPRETER_ELF so as not to change it's behavior in case someone
still relies on it.

As an aside, it seems the elf_check_arch() macros should really be checking
for more than a valid e_machine value.  I'd think checking one or more of
the e_ident[EI_CLASS], e_ident[EI_DATA] and e_ident[EI_OSABI] values would
be required as well, no?

fs/binfmt_elf.c

@@ -602,6 +602,10 @@ static int load_elf_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 			// printk(KERN_WARNING "ELF: Ambiguous type, using ELF\n");
 			interpreter_type = INTERPRETER_ELF;
 		}
+		/* Verify the interpreter has a valid arch */
+		if ((interpreter_type == INTERPRETER_ELF) &&
+		    !elf_check_arch(&interp_elf_ex))
+			goto out_free_dentry;
 	} else {
 		/* Executables without an interpreter also need a personality  */
 		SET_PERSONALITY(elf_ex, ibcs2_interpreter);