Fix permission checks in EXT2.

CMakeLists.txt

@@ -79,6 +79,8 @@ add_custom_target(filesystem
     COMMAND echo "---------------------------------------------"
     COMMAND echo "Creating EXT2 filesystem..."
     COMMAND echo "---------------------------------------------"
+    COMMAND mkdir -p ${CMAKE_SOURCE_DIR}/files/proc
+    COMMAND mkdir -p ${CMAKE_SOURCE_DIR}/files/dev
     COMMAND mke2fs -L 'rootfs' -N 0 -d ${CMAKE_SOURCE_DIR}/files -m 5 -r 1 -t ext2 -v -F ${CMAKE_BINARY_DIR}/rootfs.img 32M
     COMMAND echo "---------------------------------------------"
     COMMAND echo "Done!"

libc/src/strerror.c

@@ -15,6 +15,11 @@ char *strerror(int errnum)
     case 0:
         strcpy(error, "Success");
         break;
+#ifdef EPERM
+    case EPERM:
+        strcpy(error, "Operation not permitted");
+        break;
+#endif
 #ifdef ENOENT
     case ENOENT:
         strcpy(error, "No such file or directory");

mentos/src/fs/ext2.c

@@ -461,6 +461,44 @@ static const char *time_to_string(uint32_t time)
     return s;
 }
 
+/// @brief Checks if the requests in flags are valid.
+/// @param flags the flags to check.
+/// @param mask the mask to check against.
+/// @param uid the uid of the owner.
+/// @param gid the gid of the owner.
+/// @return true on success, false otherwise.
+static bool_t ext2_valid_permissions(int flags, mode_t mask, uid_t uid, gid_t gid)
+{
+    // Check the permissions.
+    task_struct *task = scheduler_get_current_process();
+    // The current task is the owner.
+    if (task->uid == uid) {
+        if (!bitmask_check(mask, S_IRUSR))
+            return false;
+        if (bitmask_check(flags, O_WRONLY) && !bitmask_check(mask, S_IWUSR))
+            return false;
+        if (bitmask_check(flags, O_RDWR) && (!bitmask_check(mask, S_IRUSR) || !bitmask_check(mask, S_IWUSR)))
+            return false;
+    }
+    if (task->gid == gid) {
+        if (!bitmask_check(mask, S_IRGRP))
+            return false;
+        if (bitmask_check(flags, O_WRONLY) && !bitmask_check(mask, S_IWGRP))
+            return false;
+        if (bitmask_check(flags, O_RDWR) && (!bitmask_check(mask, S_IRGRP) || !bitmask_check(mask, S_IWGRP)))
+            return false;
+    }
+    if ((task->uid != uid) && (task->gid != gid)) {
+        if (!bitmask_check(mask, S_IROTH))
+            return false;
+        if (bitmask_check(flags, O_WRONLY) && !bitmask_check(mask, S_IWOTH))
+            return false;
+        if (bitmask_check(flags, O_RDWR) && (!bitmask_check(mask, S_IROTH) || !bitmask_check(mask, S_IWOTH)))
+            return false;
+    }
+    return true;
+}
+
 /// @brief Dumps on debugging output the superblock.
 /// @param sb the object to dump.
 static void ext2_dump_superblock(ext2_superblock_t *sb)
@@ -2254,6 +2292,7 @@ static vfs_file_t *ext2_open(const char *path, int flags, mode_t mode)
             return ext2_creat(path, mode);
         } else {
             pr_err("The file does not exist `%s`.\n", absolute_path);
+            errno = ENOENT;
             return NULL;
         }
     }
@@ -2265,6 +2304,12 @@ static vfs_file_t *ext2_open(const char *path, int flags, mode_t mode)
         pr_err("Failed to read the inode of `%s`.\n", direntry.name);
         return NULL;
     }
+
+    if (!ext2_valid_permissions(flags, inode.mode, inode.uid, inode.gid)) {
+        errno = EACCES;
+        return NULL;
+    }
+
     vfs_file_t *file = ext2_find_vfs_file_with_inode(fs, direntry.inode);
     if (file == NULL) {
         // Allocate the memory for the file.
@@ -2280,8 +2325,6 @@ static vfs_file_t *ext2_open(const char *path, int flags, mode_t mode)
         // Add the vfs_file to the list of associated files.
         list_head_add_tail(&file->siblings, &fs->opened_files);
     }
-    pr_debug("ext2_open(path: \"%s\", flags: %d, mode: %d) -> file(ino: %d, name: \"%s\")\n",
-             path, flags, mode, file->ino, file->name);
     return file;
 }
 

mentos/src/fs/vfs.c

@@ -143,7 +143,7 @@ vfs_file_t *vfs_open(const char *path, int flags, mode_t mode)
     // Retrieve the file.
     vfs_file_t *file = sb_root->fs_operations->open_f(absolute_path, flags, mode);
     if (file == NULL) {
-        pr_err("vfs_open(%s): Cannot find the given file (%s)!\n", path, strerror(errno));
+        pr_debug("vfs_open(%s): Filesystem open returned NULL file (errno: %d, %s)!\n", path, errno, strerror(errno));
         return NULL;
     }
     // Increment file reference counter.

mentos/src/klib/strerror.c

@@ -15,6 +15,11 @@ char *strerror(int errnum)
     case 0:
         strcpy(error, "Success");
         break;
+#ifdef EPERM
+    case EPERM:
+        strcpy(error, "Operation not permitted");
+        break;
+#endif
 #ifdef ENOENT
     case ENOENT:
         strcpy(error, "No such file or directory");

programs/cat.c

@@ -9,32 +9,54 @@
 #include <string.h>
 #include <sys/unistd.h>
 #include <strerror.h>
+#include <sys/stat.h>
 
 int main(int argc, char **argv)
 {
-    if (argc != 2) {
-        printf("%s: missing operand.\n", argv[0]);
-        printf("Try '%s --help' for more information.\n\n", argv[0]);
+    if (argc < 2) {
+        printf("cat: missing operand.\n");
+        printf("Try 'cat --help' for more information.\n\n");
         return 1;
     }
-    if (strcmp(argv[1], "--help") == 0) {
-        printf("Prints the content of the given file.\n");
-        printf("Usage:\n");
-        printf("    %s <file>\n\n", argv[0]);
-        return 0;
-    }
-    int fd = open(argv[1], O_RDONLY, 42);
-    if (fd < 0) {
-        printf("%s: %s: %s\n\n", argv[0], strerror(errno), argv[1]);
-        return 1;
+    // Check if `--help` is provided.
+    for (int i = 1; i < argc; ++i) {
+        if (strcmp(argv[i], "--help") == 0) {
+            printf("Prints the content of the given file.\n");
+            printf("Usage:\n");
+            printf("    cat <file>\n\n");
+            return 0;
+        }
     }
+    // Prepare the buffer for reading.
     char buffer[BUFSIZ];
-    // Put on the standard output the characters.
-    while (read(fd, buffer, BUFSIZ) > 0) {
-        puts(buffer);
+    // Iterate the arguments.
+    for (int i = 1; i < argc; ++i) {
+        int fd = open(argv[i], O_RDONLY, 42);
+        if (fd < 0) {
+            printf("cat: %s: %s\n\n", argv[i], strerror(errno));
+            continue;
+        }
+        stat_t statbuf;
+        if (fstat(fd, &statbuf) == -1) {
+            printf("cat: %s: %s\n\n", argv[i], strerror(errno));
+            // Close the file descriptor.
+            close(fd);
+            continue;
+        }
+        if (S_ISDIR(statbuf.st_mode)) {
+            printf("cat: %s: %s\n\n", argv[i], strerror(EISDIR));
+            // Close the file descriptor.
+            close(fd);
+            continue;
+        }
+        // Put on the standard output the characters.
+        while (read(fd, buffer, BUFSIZ) > 0) {
+            puts(buffer);
+        }
+        // Close the file descriptor.
+        close(fd);
     }
     putchar('\n');
     putchar('\n');
-    close(fd);
     return 0;
 }

programs/ls.c

@@ -145,7 +145,7 @@ int main(int argc, char *argv[])
         no_directory = false;
         int fd       = open(argv[i], O_RDONLY | O_DIRECTORY, 0);
         if (fd == -1) {
-            printf("%s: cannot access '%s': %s\n\n", argv[0], argv[i], strerror(errno));
+            printf("ls: cannot access '%s': %s\n\n", argv[i], strerror(errno));
         } else {
             printf("%s:\n", argv[i]);
             print_ls(fd, argv[i], flags);
@@ -157,7 +157,7 @@ int main(int argc, char *argv[])
         getcwd(cwd, PATH_MAX);
         int fd = open(cwd, O_RDONLY | O_DIRECTORY, 0);
         if (fd == -1) {
-            printf("%s: cannot access '%s': %s\n\n", argv[0], cwd, strerror(errno));
+            printf("ls: cannot access '%s': %s\n\n", cwd, strerror(errno));
         } else {
             print_ls(fd, cwd, flags);
             close(fd);