Fix high-severity bugs

[jserv]

Bug fixes:

• bitmap.h: Return 0 instead of -EIO on sb_bread failure (type mismatch) Also restore bitmap and block count on allocation failure
• inode.c: Fix buffer leak in simplefs_lookup() - release bh on error
• inode.c: Initialize fi variable and use explicit indices in simplefs_set_file_into_dir() to prevent undefined behavior
• inode.c: Add null termination after strncpy for filenames
• inode.c: Add bounds validation for extent avail index in simplefs_create(), simplefs_link(), and simplefs_symlink()
• inode.c: Add missing extent nr_files increment in link/symlink

In addition, this commit adds Linux 6.15+ compatibility.

• Update write_begin() signature (kiocb-based API)
• Update write_end() signature and file reference access
• Conditionally exclude writepage from aops (deprecated)
• Update simplefs_mkdir() to return 'struct dentry *'

---

Summary by cubic

Fixes high-severity SimpleFS bugs that could leak buffers, corrupt directory entries, or mis-handle block allocation. Adds Linux 6.15+ compatibility for write paths and mkdir to keep builds green and runtime stable.

• Bug Fixes

  • Allocation: on sb_bread failure, restore bitmap and free-block count, and return 0 (reserved) instead of -EIO.
  • simplefs_lookup: release buffer on error to avoid a leak.
  • Directory entries: initialize indices and null-terminate filenames after strncpy to prevent undefined behavior.
  • Extents: validate avail index in create/link/symlink and increment extent nr_files in link/symlink.

• Compatibility

  • Update write_begin/write_end to 6.15+ kiocb signatures, adjust inode/file access, and keep older branches; add space checks before block_write_begin.
  • Drop writepage from aops on 6.15+ (deprecated).
  • simplefs_mkdir returns struct dentry* on 6.15+.

^{Written for commit fe5f56b. Summary will update automatically on new commits.}

[cubic-dev-ai]

1 issue found across 3 files

Prompt for AI agents (all 1 issues)

Understand the root cause of the following 1 issues and fix them.


<file name="inode.c">

<violation number="1" location="inode.c:1030">
Returning -EMLINK via the new `avail &gt;= SIMPLEFS_MAX_EXTENTS` branch leaks the inode allocated by `simplefs_new_inode()` because the `goto end` path never frees the inode or its block.</violation>
</file>

_{Reply to cubic to teach it or ask questions. Re-run a review with @cubic-dev-ai review this PR}

[cubic-dev-ai]

Returning -EMLINK via the new avail >= SIMPLEFS_MAX_EXTENTS branch leaks the inode allocated by simplefs_new_inode() because the goto end path never frees the inode or its block.

Prompt for AI agents

Address the following comment on inode.c at line 1030:

<comment>Returning -EMLINK via the new `avail &gt;= SIMPLEFS_MAX_EXTENTS` branch leaks the inode allocated by `simplefs_new_inode()` because the `goto end` path never frees the inode or its block.</comment>

<file context>
@@ -1003,6 +1024,12 @@ static int simplefs_link(struct dentry *old_dentry,
+    /* Validate avail index is within bounds */
+    if (avail &gt;= SIMPLEFS_MAX_EXTENTS) {
+        ret = -EMLINK;
+        goto end;
+    }
+
</file context>