[LibOS,Pal] Fix operations on files without permissions

This commit fixes the problem in which the user is not allowed to
manipulate (unlink, chmod) files without read permissions. Because PAL
requires us to open such files, we override the host mode in order to be
able to open them.

Signed-off-by: Paweł Marczewski <pawel@invisiblethingslab.com>

LibOS/shim/src/fs/chroot/fs.c

@@ -21,6 +21,7 @@
 
 #include "pal.h"
 #include "pal_error.h"
+#include "perm.h"
 #include "shim_flags_conv.h"
 #include "shim_fs.h"
 #include "shim_handle.h"
@@ -33,6 +34,17 @@
 
 #define KEEP_URI_PREFIX 0
 
+/*
+ * Always add a read permission to files created on host, because PAL requires opening the file even
+ * for operations such as `unlink` or `chmod`.
+ *
+ * The updated file permissions will not be visible to the process creating the file or updating its
+ * permissions, e.g. if a process creates a write-only file, Gramine's `stat` will still report it
+ * as write-only. However, other Gramine processes accessing that file afterwards will see the
+ * updated permissions.
+ */
+#define HOST_PERM(perm) ((perm) | PERM_r________)
+
 static int chroot_mount(const char* uri, void** mount_data) {
     __UNUSED(mount_data);
     if (!(strstartswith(uri, URI_PREFIX_FILE) || strstartswith(uri, URI_PREFIX_DEV)))
@@ -215,7 +227,7 @@ static int chroot_temp_open(struct shim_dentry* dent, mode_t type, PAL_HANDLE* o
 
 /* Open a PAL handle, and associate it with a LibOS handle (if provided). */
 static int chroot_do_open(struct shim_handle* hdl, struct shim_dentry* dent, mode_t type,
-                          int flags, mode_t mode) {
+                          int flags, mode_t perm) {
     assert(locked(&dent->lock));
 
     int ret;
@@ -229,7 +241,8 @@ static int chroot_do_open(struct shim_handle* hdl, struct shim_dentry* dent, mod
     int access = LINUX_OPEN_FLAGS_TO_PAL_ACCESS(flags);
     int create = LINUX_OPEN_FLAGS_TO_PAL_CREATE(flags);
     int options = LINUX_OPEN_FLAGS_TO_PAL_OPTIONS(flags);
-    ret = DkStreamOpen(uri, access, mode, create, options, &palhdl);
+    mode_t host_perm = HOST_PERM(perm);
+    ret = DkStreamOpen(uri, access, host_perm, create, options, &palhdl);
     if (ret < 0) {
         ret = pal_to_unix_errno(ret);
         goto out;
@@ -266,7 +279,7 @@ static int chroot_open(struct shim_handle* hdl, struct shim_dentry* dent, int fl
         goto out;
     }
 
-    ret = chroot_do_open(hdl, dent, dent->type, flags, /*mode=*/0);
+    ret = chroot_do_open(hdl, dent, dent->type, flags, /*perm=*/0);
     if (ret < 0)
         goto out;
 
@@ -681,7 +694,8 @@ static int chroot_chmod(struct shim_dentry* dent, mode_t perm) {
     if (ret < 0)
         goto out;
 
-    PAL_STREAM_ATTR attr = {.share_flags = perm};
+    mode_t host_perm = HOST_PERM(perm);
+    PAL_STREAM_ATTR attr = {.share_flags = host_perm};
     ret = DkStreamAttributesSetByHandle(palhdl, &attr);
     DkObjectClose(palhdl);
     if (ret < 0) {

LibOS/shim/test/ltp/ltp.cfg

@@ -219,22 +219,6 @@ skip = yes
 [dirtyc0w]
 skip = yes
 
-# Subtest 4 tries to unlink a file which is not readable. See
-# https://github.com/oscarlab/graphene/issues/1248.
-[dup07]
-must-pass =
-    1
-    2
-    3
-
-# Subtest 4 tries to unlink a file which is not readable. See
-# https://github.com/oscarlab/graphene/issues/1248.
-[dup202]
-must-pass =
-    1
-    2
-    3
-
 # complex test, not all of its checking is implemented in Graphene
 [epoll01]
 skip = yes
@@ -428,15 +412,6 @@ skip = yes
 [fcntl26_64]
 skip = yes
 
-# 2. unlink in /tmp fails with EACCES
-[fcntl28]
-must-pass =
-    1
-
-[fcntl28_64]
-must-pass =
-    1
-
 # no F_GETPIPE_SZ
 [fcntl30]
 skip = yes

Pal/src/host/Linux-SGX/db_files.c

@@ -777,7 +777,7 @@ static int file_attrquerybyhdl(PAL_HANDLE handle, PAL_STREAM_ATTR* attr) {
 
 static int file_attrsetbyhdl(PAL_HANDLE handle, PAL_STREAM_ATTR* attr) {
     int fd  = handle->file.fd;
-    int ret = ocall_fchmod(fd, attr->share_flags | PERM_rw_______);
+    int ret = ocall_fchmod(fd, attr->share_flags);
     if (ret < 0)
         return unix_to_pal_error(ret);
 

Pal/src/host/Linux/db_files.c

@@ -248,7 +248,7 @@ static int file_attrquerybyhdl(PAL_HANDLE handle, PAL_STREAM_ATTR* attr) {
 static int file_attrsetbyhdl(PAL_HANDLE handle, PAL_STREAM_ATTR* attr) {
     int fd = handle->generic.fds[0], ret;
 
-    ret = DO_SYSCALL(fchmod, fd, attr->share_flags | PERM_rw_______);
+    ret = DO_SYSCALL(fchmod, fd, attr->share_flags);
     if (ret < 0)
         return unix_to_pal_error(ret);