fdpic: check that the size returned by kernel_read() is what we asked for

Check that the size of the read returned by kernel_read() is what we asked
for.  If it isn't, then reject the binary as being a badly formatted.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/binfmt_elf_fdpic.c

@@ -136,8 +136,8 @@ static int elf_fdpic_fetch_phdrs(struct elf_fdpic_params *params,
 
 	retval = kernel_read(file, params->hdr.e_phoff,
 			     (char *) params->phdrs, size);
-	if (retval < 0)
-		return retval;
+	if (unlikely(retval != size))
+		return retval < 0 ? retval : -ENOEXEC;
 
 	/* determine stack size for this binary */
 	phdr = params->phdrs;
@@ -218,8 +218,11 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm,
 					     phdr->p_offset,
 					     interpreter_name,
 					     phdr->p_filesz);
-			if (retval < 0)
+			if (unlikely(retval != phdr->p_filesz)) {
+				if (retval >= 0)
+					retval = -ENOEXEC;
 				goto error;
+			}
 
 			retval = -ENOENT;
 			if (interpreter_name[phdr->p_filesz - 1] != '\0')
@@ -245,8 +248,11 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm,
 
 			retval = kernel_read(interpreter, 0, bprm->buf,
 					     BINPRM_BUF_SIZE);
-			if (retval < 0)
+			if (unlikely(retval != BINPRM_BUF_SIZE)) {
+				if (retval >= 0)
+					retval = -ENOEXEC;
 				goto error;
+			}
 
 			interp_params.hdr = *((struct elfhdr *) bprm->buf);
 			break;