FAILED: patch "[PATCH] jbd2: fix integer underflow in" failed to apply to 5.10-stable tree

FAILED: patch "[PATCH] jbd2: fix integer underflow in" failed to apply to 5.10-stable tree

[gregkh]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 289a2ca0c9b7eae74f93fc213b0b971669b8683d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026072041-pork-untapped-b293@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 289a2ca0c9b7eae74f93fc213b0b971669b8683d Mon Sep 17 00:00:00 2001
From: Junrui Luo <moonafterrain@outlook.com>
Date: Wed, 13 May 2026 17:28:40 +0800
Subject: [PATCH] jbd2: fix integer underflow in
 jbd2_journal_initialize_fast_commit()

jbd2_journal_initialize_fast_commit() validates journal capacity by
checking (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS).
Both j_last and num_fc_blks are unsigned, so when num_fc_blks exceeds
j_last the subtraction wraps to a large value, bypassing the bounds
check.

The resulting underflow corrupts j_last, j_fc_first, and j_free,
leading to journal abort.

Fix by checking num_fc_blks against j_last before the subtraction,
returning -EFSCORRUPTED.

Fixes: 6866d7b3f2bb ("ext4 / jbd2: add fast commit initialization")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Fixes: e029c5f27987 ("ext4: make num of fast commit blocks configurable")
Reviewed-by: Baokun Li <libaokun@linux.alibaba.com>
Fixes: e029c5f279872 ("ext4: make num of fast commit blocks configurable")
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/SYBPR01MB7881663C927DE9D7BBF4D1DFAF062@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 4f397fcdb13c..e3b2e38e1a1b 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -2263,6 +2263,8 @@ jbd2_journal_initialize_fast_commit(journal_t *journal)
 	unsigned long long num_fc_blks;
 
 	num_fc_blks = jbd2_journal_get_num_fc_blks(sb);
+	if (num_fc_blks > journal->j_last)
+		return -EFSCORRUPTED;
 	if (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS)
 		return -ENOSPC;
 

[PATCH 5.10.y 1/2] jbd2: add a helper to find out number of fast commit blocks

[Sasha Levin]

From: Harshad Shirwadkar <harshadshirwadkar@gmail.com>

[ Upstream commit 9bd23c31f392bda88618008f27fd52ee9e0fac38 ]

Add a helper to read number of fast commit blocks from jbd2 superblock
and also rename the JBD2_MIN_FC_BLKS to
JBD2_DEFAULT_FAST_COMMIT_BLOCKS since this constant is just the
default number of fast commit blocks to use in case number of fast
commit blocks isn't set in jbd2 superblock.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20201120202232.2240293-2-harshadshirwadkar@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Stable-dep-of: 289a2ca0c9b7 ("jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/jbd2/journal.c    | 8 ++------
 include/linux/jbd2.h | 9 ++++++++-
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 14b176d63482df..cbf56b18521666 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1884,9 +1884,7 @@ static int load_superblock(journal_t *journal)
 
 	if (jbd2_has_feature_fast_commit(journal)) {
 		journal->j_fc_last = be32_to_cpu(sb->s_maxlen);
-		num_fc_blocks = be32_to_cpu(sb->s_num_fc_blks);
-		if (!num_fc_blocks)
-			num_fc_blocks = JBD2_MIN_FC_BLOCKS;
+		num_fc_blocks = jbd2_journal_get_num_fc_blks(sb);
 		if (journal->j_last - num_fc_blocks >= JBD2_MIN_JOURNAL_BLOCKS)
 			journal->j_last = journal->j_fc_last - num_fc_blocks;
 		journal->j_fc_first = journal->j_last + 1;
@@ -2117,9 +2115,7 @@ jbd2_journal_initialize_fast_commit(journal_t *journal)
 	journal_superblock_t *sb = journal->j_superblock;
 	unsigned long long num_fc_blks;
 
-	num_fc_blks = be32_to_cpu(sb->s_num_fc_blks);
-	if (num_fc_blks == 0)
-		num_fc_blks = JBD2_MIN_FC_BLOCKS;
+	num_fc_blks = jbd2_journal_get_num_fc_blks(sb);
 	if (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS)
 		return -ENOSPC;
 
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 80f573d1b3b83b..f5826f99fe9aa1 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -68,7 +68,7 @@ extern void *jbd2_alloc(size_t size, gfp_t flags);
 extern void jbd2_free(void *ptr, size_t size);
 
 #define JBD2_MIN_JOURNAL_BLOCKS 1024
-#define JBD2_MIN_FC_BLOCKS	256
+#define JBD2_DEFAULT_FAST_COMMIT_BLOCKS 256
 
 #ifdef __KERNEL__
 
@@ -1686,6 +1686,13 @@ static inline int jbd2_journal_has_csum_v2or3(journal_t *journal)
 	return journal->j_chksum_driver != NULL;
 }
 
+static inline int jbd2_journal_get_num_fc_blks(journal_superblock_t *jsb)
+{
+	int num_fc_blocks = be32_to_cpu(jsb->s_num_fc_blks);
+
+	return num_fc_blocks ? num_fc_blocks : JBD2_DEFAULT_FAST_COMMIT_BLOCKS;
+}
+
 /*
  * Return number of free blocks in the log. Must be called under j_state_lock.
  */
-- 
2.53.0

[PATCH 5.10.y 2/2] jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit()

[Sasha Levin]

From: Junrui Luo <moonafterrain@outlook.com>

[ Upstream commit 289a2ca0c9b7eae74f93fc213b0b971669b8683d ]

jbd2_journal_initialize_fast_commit() validates journal capacity by
checking (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS).
Both j_last and num_fc_blks are unsigned, so when num_fc_blks exceeds
j_last the subtraction wraps to a large value, bypassing the bounds
check.

The resulting underflow corrupts j_last, j_fc_first, and j_free,
leading to journal abort.

Fix by checking num_fc_blks against j_last before the subtraction,
returning -EFSCORRUPTED.

Fixes: 6866d7b3f2bb ("ext4 / jbd2: add fast commit initialization")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Fixes: e029c5f27987 ("ext4: make num of fast commit blocks configurable")
Reviewed-by: Baokun Li <libaokun@linux.alibaba.com>
Fixes: e029c5f279872 ("ext4: make num of fast commit blocks configurable")
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/SYBPR01MB7881663C927DE9D7BBF4D1DFAF062@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/jbd2/journal.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index cbf56b18521666..526d2971f12e5e 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -2116,6 +2116,8 @@ jbd2_journal_initialize_fast_commit(journal_t *journal)
 	unsigned long long num_fc_blks;
 
 	num_fc_blks = jbd2_journal_get_num_fc_blks(sb);
+	if (num_fc_blks > journal->j_last)
+		return -EFSCORRUPTED;
 	if (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS)
 		return -ENOSPC;
 
-- 
2.53.0