5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> [ Upstream commit 9403001ad65ae4f4c5de368bdda3a0636b51d51a ] Patch series "nilfs2: fix potential issues with empty b-tree nodes". This series addresses three potential issues with empty b-tree nodes that can occur with corrupted filesystem images, including one recently discovered by syzbot. This patch (of 3): If a b-tree is broken on the device, and the b-tree height is greater than 2 (the level of the root node is greater than 1) even if the number of child nodes of the b-tree root is 0, a NULL pointer dereference occurs in nilfs_btree_prepare_insert(), which is called from nilfs_btree_insert(). This is because, when the number of child nodes of the b-tree root is 0, nilfs_btree_do_lookup() does not set the block buffer head in any of path[x].bp_bh, leaving it as the initial value of NULL, but if the level of the b-tree root node is greater than 1, nilfs_btree_get_nonroot_node(), which accesses the buffer memory of path[x].bp_bh, is called. Fix this issue by adding a check to nilfs_btree_root_broken(), which performs sanity checks when reading the root node from the device, to detect this inconsistency. Thanks to Lizhi Xu for trying to solve the bug and clarifying the cause early on. Link: https://lkml.kernel.org/r/20240904081401.16682-1-konishi.ryusuke@xxxxxxxxx Link: https://lkml.kernel.org/r/20240902084101.138971-1-lizhi.xu@xxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20240904081401.16682-2-konishi.ryusuke@xxxxxxxxx Fixes: 17c76b0104e4 ("nilfs2: B-tree based block mapping") Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Reported-by: syzbot+9bff4c7b992038a7409f@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=9bff4c7b992038a7409f Cc: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- fs/nilfs2/btree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c index 8e3d343b9a793..fbb6ec56843f4 100644 --- a/fs/nilfs2/btree.c +++ b/fs/nilfs2/btree.c @@ -381,7 +381,8 @@ static int nilfs_btree_root_broken(const struct nilfs_btree_node *node, if (unlikely(level < NILFS_BTREE_LEVEL_NODE_MIN || level >= NILFS_BTREE_LEVEL_MAX || nchildren < 0 || - nchildren > NILFS_BTREE_ROOT_NCHILDREN_MAX)) { + nchildren > NILFS_BTREE_ROOT_NCHILDREN_MAX || + (nchildren == 0 && level > NILFS_BTREE_LEVEL_NODE_MIN))) { nilfs_crit(inode->i_sb, "bad btree root (ino=%lu): level = %d, flags = 0x%x, nchildren = %d", inode->i_ino, level, flags, nchildren); -- 2.43.0
