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ext4: only dirty folios when data journaling regular files 

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: d84c9ebdac ("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>
(cherry picked from commit cf6a4c4ac7b6e3214f25df594c9689a62f1bb456)
This commit is contained in:
Brian Foster 2025-05-16 13:38:00 -04:00 committed by Wentao Guan
parent c0019b1bd8
commit ec3c16cd9a
1 changed files with 6 additions and 1 deletions
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7
fs/ext4/inode.c
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@ -1011,7 +1011,12 @@ int ext4_walk_page_buffers(handle_t *handle, struct inode *inode,
*/
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);
}