[PATCH AUTOSEL 6.16-5.4] jfs: truncate good inode pages when hard link is 0

[Sasha Levin <sashal@kernel.org>]

From: Lizhi Xu <lizhi.xu@windriver.com>

[ Upstream commit 2d91b3765cd05016335cd5df5e5c6a29708ec058 ]

The fileset value of the inode copy from the disk by the reproducer is
AGGR_RESERVED_I. When executing evict, its hard link number is 0, so its
inode pages are not truncated. This causes the bugon to be triggered when
executing clear_inode() because nrpages is greater than 0.

Reported-by: syzbot+6e516bb515d93230bc7b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6e516bb515d93230bc7b
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

**Backport Status: YES**

This commit should be backported to stable kernel trees based on the
following extensive analysis:

## Critical Bug Fix Nature

This commit fixes a kernel BUG_ON() crash that can be triggered in
production systems. Looking at the code changes and commit message:

1. **The Bug**: When JFS evicts an inode with `fileset ==
   AGGR_RESERVED_I` and hard link count of 0, the inode pages were not
   being truncated. This leads to a BUG_ON() trigger in `clear_inode()`
   at fs/inode.c when checking `BUG_ON(inode->i_data.nrpages)`.

2. **Root Cause**: The original code only called
   `truncate_inode_pages_final()` for inodes with `fileset ==
   FILESYSTEM_I`, missing other fileset types like `AGGR_RESERVED_I`.
   This left pages in memory when they should have been freed.

## Fix Characteristics

The fix is ideal for stable backporting:

1. **Minimal and Contained**: The change is just moving one line of code
   - `truncate_inode_pages_final(&inode->i_data)` is moved outside the
   `if (JFS_IP(inode)->fileset == FILESYSTEM_I)` condition block,
   ensuring it runs for ALL inodes with 0 hard links, not just
   FILESYSTEM_I inodes.

2. **Low Risk**: The change ensures proper cleanup for all inode types
   during eviction, which is the expected behavior. The function
   `truncate_inode_pages_final()` is safe to call for any inode being
   evicted with no links.

3. **Clear Bug Report**: This fixes a syzbot-reported crash with a
   reproducible test case
   (syzbot+6e516bb515d93230bc7b@syzkaller.appspotmail.com).

## Impact Analysis

- **User Impact**: Without this fix, users can experience kernel
  panics/crashes when specific JFS inode conditions occur
- **Security**: Prevents potential denial-of-service through triggerable
  BUG_ON()
- **Regression Risk**: Minimal - the change ensures proper cleanup that
  should have been happening all along

## Historical Context

Looking at related commits:
- Similar eviction-related fixes have been backported (e.g.,
  e0e1958f4c36 "jfs: fix uaf in jfs_evict_inode")
- JFS has had multiple stability fixes in the eviction path that were
  deemed stable-worthy
- The subsystem maintainer (Dave Kleikamp) signed off on this fix

The commit clearly meets stable kernel criteria: it fixes a real bug
that causes system crashes, the fix is minimal and correct, and there's
no risk of introducing new features or architectural changes.

 fs/jfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/jfs/inode.c b/fs/jfs/inode.c
index 60fc92dee24d..81e6b18e81e1 100644
--- a/fs/jfs/inode.c
+++ b/fs/jfs/inode.c
@@ -145,9 +145,9 @@ void jfs_evict_inode(struct inode *inode)
 	if (!inode->i_nlink && !is_bad_inode(inode)) {
 		dquot_initialize(inode);
 
+		truncate_inode_pages_final(&inode->i_data);
 		if (JFS_IP(inode)->fileset == FILESYSTEM_I) {
 			struct inode *ipimap = JFS_SBI(inode->i_sb)->ipimap;
-			truncate_inode_pages_final(&inode->i_data);
 
 			if (test_cflag(COMMIT_Freewmap, inode))
 				jfs_free_zero_link(inode);
-- 
2.39.5