vfs: Force truncation even without permissions

O_TRUNC as a mode does not seem to imply write permissions
but we still wish to truncate the file before giving back a file
descriptor. Therefore the kernel can now override any permission checks
if it wishes to do a truncation while still using the "ordinary path".

3 files changed, 5 insertions, 5 deletions

diff --git a/kernel/cpu/syscall.c b/kernel/cpu/syscall.c
index 284a80d..a78e63e 100644
--- a/kernel/cpu/syscall.c
+++ b/kernel/cpu/syscall.c
@@ -152,7 +152,7 @@ int syscall_fstat(int fd, struct stat *buf) {
 }
 
 int syscall_ftruncate(int fd, size_t length) {
-  return vfs_ftruncate(fd, length);
+  return vfs_ftruncate(fd, length, 0);
 }
 
 char *syscall_getcwd(char *buf, size_t size) {
diff --git a/kernel/fs/vfs.c b/kernel/fs/vfs.c
index c06c71f..3b912ce 100644
--- a/kernel/fs/vfs.c
+++ b/kernel/fs/vfs.c
@@ -289,7 +289,7 @@ int vfs_open(const char *file, int flags, int mode) {
   // FIXME: Maybe it is sometimes a TTY?
   int rc = vfs_create_fd(flags, mode, 0 /*is_tty*/, inode, NULL);
   if (flags & O_TRUNC) {
-    vfs_ftruncate(rc, 0);
+    vfs_ftruncate(rc, 0, 1);
   }
   return rc;
 }
@@ -488,12 +488,12 @@ int vfs_dup2(int org_fd, int new_fd) {
   return 1;
 }
 
-int vfs_ftruncate(int fd, size_t length) {
+int vfs_ftruncate(int fd, size_t length, int force_truncate) {
   vfs_fd_t *fd_ptr = get_vfs_fd(fd, NULL);
   if (!fd_ptr) {
     return -EBADF;
   }
-  if (!(fd_ptr->flags & O_READ)) {
+  if (!(fd_ptr->flags & O_WRITE) && !force_truncate) {
     return -EINVAL;
   }
   vfs_inode_t *inode = fd_ptr->inode;
diff --git a/kernel/fs/vfs.h b/kernel/fs/vfs.h
index cb1c885..98220d3 100644
--- a/kernel/fs/vfs.h
+++ b/kernel/fs/vfs.h
@@ -86,7 +86,7 @@ vfs_inode_t *vfs_internal_open(const char *file);
 int vfs_mkdir(const char *path, int mode);
 int vfs_create_fd(int flags, int mode, int is_tty, vfs_inode_t *inode,
                   vfs_fd_t **fd);
-int vfs_ftruncate(int fd, size_t length);
+int vfs_ftruncate(int fd, size_t length, int force_truncate);
 int vfs_chdir(const char *path);
 int vfs_fstat(int fd, struct stat *buf);
 vfs_inode_t *vfs_create_inode(