From 5bc09b397cbf1221f8a8aacb1152650c9195b02b Mon Sep 17 00:00:00 2001
From: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Date: Sun, 4 Feb 2024 01:16:45 +0900
Subject: [PATCH] nilfs2: fix potential bug in end_buffer_async_write
Git-commit: 5bc09b397cbf1221f8a8aacb1152650c9195b02b
Patch-mainline: v6.8-rc4
References: bsc#1222437 CVE-2024-26685
According to a syzbot report, end_buffer_async_write(), which handles the
completion of block device writes, may detect abnormal condition of the
buffer async_write flag and cause a BUG_ON failure when using nilfs2.
Nilfs2 itself does not use end_buffer_async_write(). But, the async_write
flag is now used as a marker by commit 7f42ec394156 ("nilfs2: fix issue
with race condition of competition between segments for dirty blocks") as
a means of resolving double list insertion of dirty blocks in
nilfs_lookup_dirty_data_buffers() and nilfs_lookup_node_buffers() and the
resulting crash.
This modification is safe as long as it is used for file data and b-tree
node blocks where the page caches are independent. However, it was
irrelevant and redundant to also introduce async_write for segment summary
and super root blocks that share buffers with the backing device. This
led to the possibility that the BUG_ON check in end_buffer_async_write
would fail as described above, if independent writebacks of the backing
device occurred in parallel.
The use of async_write for segment summary buffers has already been
removed in a previous change.
Fix this issue by removing the manipulation of the async_write flag for
the remaining super root block buffer.
Link: https://lkml.kernel.org/r/20240203161645.4992-1-konishi.ryusuke@gmail.com
Fixes: 7f42ec394156 ("nilfs2: fix issue with race condition of competition between segments for dirty blocks")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+5c04210f7c7f897c1e7f@syzkaller.appspotmail.com
Closes: https://lkml.kernel.org/r/00000000000019a97c05fd42f8c8@google.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Anthony Iliopoulos <ailiop@suse.com>
---
fs/nilfs2/segment.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 9e865732d352..293dc4ff6784 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1697,7 +1697,6 @@ static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)
list_for_each_entry(bh, &segbuf->sb_payload_buffers,
b_assoc_buffers) {
- set_buffer_async_write(bh);
if (bh == segbuf->sb_super_root) {
if (bh->b_page != bd_page) {
lock_page(bd_page);
@@ -1708,6 +1707,7 @@ static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)
}
break;
}
+ set_buffer_async_write(bh);
if (bh->b_page != fs_page) {
nilfs_begin_page_io(fs_page);
fs_page = bh->b_page;
@@ -1793,7 +1793,6 @@ static void nilfs_abort_logs(struct list_head *logs, int err)
list_for_each_entry(bh, &segbuf->sb_payload_buffers,
b_assoc_buffers) {
- clear_buffer_async_write(bh);
if (bh == segbuf->sb_super_root) {
clear_buffer_uptodate(bh);
if (bh->b_page != bd_page) {
@@ -1802,6 +1801,7 @@ static void nilfs_abort_logs(struct list_head *logs, int err)
}
break;
}
+ clear_buffer_async_write(bh);
if (bh->b_page != fs_page) {
nilfs_end_page_io(fs_page, err);
fs_page = bh->b_page;
@@ -1889,8 +1889,9 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
BIT(BH_Delay) | BIT(BH_NILFS_Volatile) |
BIT(BH_NILFS_Redirected));
- set_mask_bits(&bh->b_state, clear_bits, set_bits);
if (bh == segbuf->sb_super_root) {
+ set_buffer_uptodate(bh);
+ clear_buffer_dirty(bh);
if (bh->b_page != bd_page) {
end_page_writeback(bd_page);
bd_page = bh->b_page;
@@ -1898,6 +1899,7 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
update_sr = true;
break;
}
+ set_mask_bits(&bh->b_state, clear_bits, set_bits);
if (bh->b_page != fs_page) {
nilfs_end_page_io(fs_page, 0);
fs_page = bh->b_page;
--
2.44.0