[PATCH v2 2/6] qnx6: release buffer_head on error in qnx6_block_map()

[Hui Peng <benquike@gmail.com>]

In qnx6_block_map(), when qnx6_check_blockptr(ptr) fails ("qnx6: hit
unused blockpointer.") inside the indirect block traversal loop, the
buffer_head bh read by sb_bread() is not released before returning 0,
leaving bh->b_count elevated and pinning the backing blockdev folio in
memory. Call brelse(bh) on that error path before returning 0.

Tested in QEMU against Linux 7.3.0-rc3 by mounting a crafted QNX6 image on
/dev/loop0 with a file (di_filelevels = 1) whose indirect block (block 5)
contains an unused block pointer (~0U), reading the file to trigger
"qnx6: hit unused blockpointer.", and then flushing per-CPU bh_lrus and
pagecache via /proc/sys/vm/drop_caches and POSIX_FADV_DONTNEED: on the
unfixed kernel indirect block 5 remains pinned in bd_mapping
(indirect_page5_leaked = 1), whereas on the fixed kernel indirect block 5
is released and evicted cleanly (indirect_page5_leaked = 0).

Fixes: 5d026c724220 ("fs: initial qnx6fs addition")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
Changes in v2:
- Split the qnx6_block_map() buffer_head leak fix into its own patch (2/6)
  and remove Markdown formatting from the commit message, as requested by
  Damien Le Moal.

 fs/qnx6/inode.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/qnx6/inode.c b/fs/qnx6/inode.c
index 13972c086673..9b624829520e 100644
--- a/fs/qnx6/inode.c
+++ b/fs/qnx6/inode.c
@@ -144,8 +144,10 @@ static unsigned qnx6_block_map(struct inode *inode, unsigned no)
 		levelptr = (no >> bitdelta) & mask;
 		ptr = ((__fs32 *)bh->b_data)[levelptr];
 
-		if (!qnx6_check_blockptr(ptr))
+		if (!qnx6_check_blockptr(ptr)) {
+			brelse(bh);
 			return 0;
+		}
 
 		block = qnx6_get_devblock(s, ptr);
 		brelse(bh);
-- 
2.49.0