6.12-stable review patch. If anyone has any objections, please let me know.
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From: Brian Foster bfoster@redhat.com
commit e26268ff1dcae5662c1b96c35f18cfa6ab73d9de upstream.
fstest generic/388 occasionally reproduces a crash that looks as follows:
BUG: kernel NULL pointer dereference, address: 0000000000000000 ... Call Trace: <TASK> ext4_block_zero_page_range+0x30c/0x380 [ext4] ext4_truncate+0x436/0x440 [ext4] ext4_process_orphan+0x5d/0x110 [ext4] ext4_orphan_cleanup+0x124/0x4f0 [ext4] ext4_fill_super+0x262d/0x3110 [ext4] get_tree_bdev_flags+0x132/0x1d0 vfs_get_tree+0x26/0xd0 vfs_cmd_create+0x59/0xe0 __do_sys_fsconfig+0x4ed/0x6b0 do_syscall_64+0x82/0x170 ...
This occurs when processing a symlink inode from the orphan list. The partial block zeroing code in the truncate path calls ext4_dirty_journalled_data() -> folio_mark_dirty(). The latter calls mapping->a_ops->dirty_folio(), but symlink inodes are not assigned an a_ops vector in ext4, hence the crash.
To avoid this problem, update the ext4_dirty_journalled_data() helper to only mark the folio dirty on regular files (for which a_ops is assigned). This also matches the journaling logic in the ext4_symlink() creation path, where ext4_handle_dirty_metadata() is called directly.
Fixes: d84c9ebdac1e ("ext4: Mark pages with journalled data dirty") Signed-off-by: Brian Foster bfoster@redhat.com Link: https://patch.msgid.link/20250516173800.175577-1-bfoster@redhat.com Signed-off-by: Theodore Ts'o tytso@mit.edu Reviewed-by: Jan Kara jack@suse.cz Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ext4/inode.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -1000,7 +1000,12 @@ int ext4_walk_page_buffers(handle_t *han */ static int ext4_dirty_journalled_data(handle_t *handle, struct buffer_head *bh) { - folio_mark_dirty(bh->b_folio); + struct folio *folio = bh->b_folio; + struct inode *inode = folio->mapping->host; + + /* only regular files have a_ops */ + if (S_ISREG(inode->i_mode)) + folio_mark_dirty(folio); return ext4_handle_dirty_metadata(handle, NULL, bh); }