The patch titled Subject: nilfs2: fix null-ptr-deref in block_dirty_buffer tracepoint has been added to the -mm mm-hotfixes-unstable branch. Its filename is nilfs2-fix-null-ptr-deref-in-block_dirty_buffer-tracepoint.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ryusuke Konishi konishi.ryusuke@gmail.com Subject: nilfs2: fix null-ptr-deref in block_dirty_buffer tracepoint Date: Thu, 7 Nov 2024 01:07:33 +0900

When using the "block:block_dirty_buffer" tracepoint, mark_buffer_dirty() may cause a NULL pointer dereference, or a general protection fault when KASAN is enabled.

This happens because, since the tracepoint was added in mark_buffer_dirty(), it references the dev_t member bh->b_bdev->bd_dev regardless of whether the buffer head has a pointer to a block_device structure.

In the current implementation, nilfs_grab_buffer(), which grabs a buffer to read (or create) a block of metadata, including b-tree node blocks, does not set the block device, but instead does so only if the buffer is not in the "uptodate" state for each of its caller block reading functions. However, if the uptodate flag is set on a folio/page, and the buffer heads are detached from it by try_to_free_buffers(), and new buffer heads are then attached by create_empty_buffers(), the uptodate flag may be restored to each buffer without the block device being set to bh->b_bdev, and mark_buffer_dirty() may be called later in that state, resulting in the bug mentioned above.

Fix this issue by making nilfs_grab_buffer() always set the block device of the super block structure to the buffer head, regardless of the state of the buffer's uptodate flag.

Link: https://lkml.kernel.org/r/20241106160811.3316-3-konishi.ryusuke@gmail.com Fixes: 5305cb830834 ("block: add block_{touch|dirty}_buffer tracepoint") Signed-off-by: Ryusuke Konishi konishi.ryusuke@gmail.com Cc: Tejun Heo tj@kernel.org Cc: Ubisectech Sirius bugreport@valiantsec.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/nilfs2/btnode.c | 2 -- fs/nilfs2/gcinode.c | 4 +--- fs/nilfs2/mdt.c | 1 - fs/nilfs2/page.c | 1 + 4 files changed, 2 insertions(+), 6 deletions(-)

--- a/fs/nilfs2/btnode.c~nilfs2-fix-null-ptr-deref-in-block_dirty_buffer-tracepoint +++ a/fs/nilfs2/btnode.c @@ -68,7 +68,6 @@ nilfs_btnode_create_block(struct address goto failed; } memset(bh->b_data, 0, i_blocksize(inode)); - bh->b_bdev = inode->i_sb->s_bdev; bh->b_blocknr = blocknr; set_buffer_mapped(bh); set_buffer_uptodate(bh); @@ -133,7 +132,6 @@ int nilfs_btnode_submit_block(struct add goto found; } set_buffer_mapped(bh); - bh->b_bdev = inode->i_sb->s_bdev; bh->b_blocknr = pblocknr; /* set block address for read */ bh->b_end_io = end_buffer_read_sync; get_bh(bh); --- a/fs/nilfs2/gcinode.c~nilfs2-fix-null-ptr-deref-in-block_dirty_buffer-tracepoint +++ a/fs/nilfs2/gcinode.c @@ -83,10 +83,8 @@ int nilfs_gccache_submit_read_data(struc goto out; }

- if (!buffer_mapped(bh)) { - bh->b_bdev = inode->i_sb->s_bdev; + if (!buffer_mapped(bh)) set_buffer_mapped(bh); - } bh->b_blocknr = pbn; bh->b_end_io = end_buffer_read_sync; get_bh(bh); --- a/fs/nilfs2/mdt.c~nilfs2-fix-null-ptr-deref-in-block_dirty_buffer-tracepoint +++ a/fs/nilfs2/mdt.c @@ -89,7 +89,6 @@ static int nilfs_mdt_create_block(struct if (buffer_uptodate(bh)) goto failed_bh;

- bh->b_bdev = sb->s_bdev; err = nilfs_mdt_insert_new_block(inode, block, bh, init_block); if (likely(!err)) { get_bh(bh); --- a/fs/nilfs2/page.c~nilfs2-fix-null-ptr-deref-in-block_dirty_buffer-tracepoint +++ a/fs/nilfs2/page.c @@ -63,6 +63,7 @@ struct buffer_head *nilfs_grab_buffer(st folio_put(folio); return NULL; } + bh->b_bdev = inode->i_sb->s_bdev; return bh; }

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Patches currently in -mm which might be from konishi.ryusuke@gmail.com are

nilfs2-fix-null-ptr-deref-in-block_touch_buffer-tracepoint.patch nilfs2-fix-null-ptr-deref-in-block_dirty_buffer-tracepoint.patch