As report by Wenqing Liu in bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215231 - Overview kernel NULL pointer dereference triggered in folio_mark_dirty() when mount and operate on a crafted f2fs image - Reproduce tested on kernel 5.16-rc3, 5.15.X under root 1. mkdir mnt 2. mount -t f2fs tmp1.img mnt 3. touch tmp 4. cp tmp mnt F2FS-fs (loop0): sanity_check_inode: inode (ino=49) extent info [5942, 4294180864, 4] is incorrect, run fsck to fix F2FS-fs (loop0): f2fs_check_nid_range: out-of-range nid=31340049, run fsck to fix. BUG: kernel NULL pointer dereference, address: 0000000000000000 folio_mark_dirty+0x33/0x50 move_data_page+0x2dd/0x460 [f2fs] do_garbage_collect+0xc18/0x16a0 [f2fs] f2fs_gc+0x1d3/0xd90 [f2fs] f2fs_balance_fs+0x13a/0x570 [f2fs] f2fs_create+0x285/0x840 [f2fs] path_openat+0xe6d/0x1040 do_filp_open+0xc5/0x140 do_sys_openat2+0x23a/0x310 do_sys_open+0x57/0x80 The root cause is for special file: e.g. character, block, fifo or socket file, f2fs doesn't assign address space operations pointer array for mapping->a_ops field, so, in a fuzzed image, SSA table indicates a data block belong to special file, when f2fs tries to migrate that block, it causes NULL pointer access once move_data_page() calls a_ops->set_dirty_page(). Cc: stable@xxxxxxxxxxxxxxx Reported-by: Wenqing Liu <wenqingliu0120@xxxxxxxxx> Signed-off-by: Chao Yu <chao@xxxxxxxxxx> --- fs/f2fs/gc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c index a946ce0ead34..e0bdc4361a9b 100644 --- a/fs/f2fs/gc.c +++ b/fs/f2fs/gc.c @@ -1457,7 +1457,8 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum, if (phase == 3) { inode = f2fs_iget(sb, dni.ino); - if (IS_ERR(inode) || is_bad_inode(inode)) + if (IS_ERR(inode) || is_bad_inode(inode) || + special_file(inode->i_mode)) continue; if (!down_write_trylock( -- 2.32.0
