consolidate BINPRM_FLAGS_ENFORCE_NONDUMP handling

new helper: would_dump(bprm, file).  Checks if we are allowed to
read the file and if we are not - sets ENFORCE_NODUMP.  Exported,
used in places that previously open-coded the same logics.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/binfmt_elf.c

@@ -668,8 +668,7 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 			 * mm->dumpable = 0 regardless of the interpreter's
 			 * permissions.
 			 */
-			if (file_permission(interpreter, MAY_READ) < 0)
-				bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+			would_dump(bprm, interpreter);
 
 			retval = kernel_read(interpreter, 0, bprm->buf,
 					     BINPRM_BUF_SIZE);

fs/binfmt_elf_fdpic.c

@@ -245,8 +245,7 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm,
 			 * mm->dumpable = 0 regardless of the interpreter's
 			 * permissions.
 			 */
-			if (file_permission(interpreter, MAY_READ) < 0)
-				bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+			would_dump(bprm, interpreter);
 
 			retval = kernel_read(interpreter, 0, bprm->buf,
 					     BINPRM_BUF_SIZE);

fs/binfmt_misc.c

@@ -149,8 +149,7 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 
 		/* if the binary is not readable than enforce mm->dumpable=0
 		   regardless of the interpreter's permissions */
-		if (file_permission(bprm->file, MAY_READ))
-			bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+		would_dump(bprm, bprm->file);
 
 		allow_write_access(bprm->file);
 		bprm->file = NULL;

fs/exec.c

@@ -1105,6 +1105,13 @@ out:
 }
 EXPORT_SYMBOL(flush_old_exec);
 
+void would_dump(struct linux_binprm *bprm, struct file *file)
+{
+	if (inode_permission(file->f_path.dentry->d_inode, MAY_READ) < 0)
+		bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+}
+EXPORT_SYMBOL(would_dump);
+
 void setup_new_exec(struct linux_binprm * bprm)
 {
 	int i, ch;
@@ -1144,9 +1151,10 @@ void setup_new_exec(struct linux_binprm * bprm)
 	if (bprm->cred->uid != current_euid() ||
 	    bprm->cred->gid != current_egid()) {
 		current->pdeath_signal = 0;
-	} else if (file_permission(bprm->file, MAY_READ) ||
-		   bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP) {
-		set_dumpable(current->mm, suid_dumpable);
+	} else {
+		would_dump(bprm, bprm->file);
+		if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)
+			set_dumpable(current->mm, suid_dumpable);
 	}
 
 	/*

include/linux/binfmts.h

@@ -111,6 +111,7 @@ extern int __must_check remove_arg_zero(struct linux_binprm *);
 extern int search_binary_handler(struct linux_binprm *, struct pt_regs *);
 extern int flush_old_exec(struct linux_binprm * bprm);
 extern void setup_new_exec(struct linux_binprm * bprm);
+extern void would_dump(struct linux_binprm *, struct file *);
 
 extern int suid_dumpable;
 #define SUID_DUMP_DISABLE	0	/* No setuid dumping */