[PATCH] Require mmap handler for a.out executables

Files supported by fs/proc/base.c, i.e.  /proc/<pid>/*, are not capable of
meeting the validity checks in ELF load_elf_*() handling because they have
no mmap handler which is required by ELF.  In order to stop a.out
executables being used as part of an exploit attack against /proc-related
vulnerabilities, we make a.out executables depend on ->mmap() existing.
Signed-off-by: Eugene Teo <eteo@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/binfmt_aout.c

@@ -278,6 +278,13 @@ static int load_aout_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 		return -ENOEXEC;
 	}
 
+	/*
+	 * Requires a mmap handler. This prevents people from using a.out
+	 * as part of an exploit attack against /proc-related vulnerabilities.
+	 */
+	if (!bprm->file->f_op || !bprm->file->f_op->mmap)
+		return -ENOEXEC;
+
 	fd_offset = N_TXTOFF(ex);
 
 	/* Check initial limits. This avoids letting people circumvent
@@ -476,6 +483,13 @@ static int load_aout_library(struct file *file)
 		goto out;
 	}
 
+	/*
+	 * Requires a mmap handler. This prevents people from using a.out
+	 * as part of an exploit attack against /proc-related vulnerabilities.
+	 */
+	if (!file->f_op || !file->f_op->mmap)
+		goto out;
+
 	if (N_FLAGS(ex))
 		goto out;