The rec_len field in the directory entry has to be a multiple of 4. A corrupted filesystem image can be used to hit a BUG() in ext4_rec_len_to_disk(), called from make_indexed_dir(). ------------[ cut here ]------------ kernel BUG at fs/ext4/ext4.h:2413! ... RIP: 0010:make_indexed_dir+0x53f/0x5f0 ... Call Trace: <TASK> ? add_dirent_to_buf+0x1b2/0x200 ext4_add_entry+0x36e/0x480 ext4_add_nondir+0x2b/0xc0 ext4_create+0x163/0x200 path_openat+0x635/0xe90 do_filp_open+0xb4/0x160 ? __create_object.isra.0+0x1de/0x3b0 ? _raw_spin_unlock+0x12/0x30 do_sys_openat2+0x91/0x150 __x64_sys_open+0x6c/0xa0 do_syscall_64+0x3c/0x80 entry_SYSCALL_64_after_hwframe+0x46/0xb0 The fix simply adds a call to ext4_check_dir_entry() to validate the directory entry, returning -EFSCORRUPTED if the entry is invalid. CC: stable@xxxxxxxxxxxxxxx Link: https://bugzilla.kernel.org/show_bug.cgi?id=216540 Signed-off-by: Luís Henriques <lhenriques@xxxxxxx> --- * Changes since v1: As suggested by Ted, I've removed the incorrect 'de->rec_len' check from previous version and replaced it with a call to ext4_check_dir_entry() instead, which is a much more complete verification. fs/ext4/namei.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index 3a31b662f661..ed76e89ffbe9 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -2254,8 +2254,16 @@ static int make_indexed_dir(handle_t *handle, struct ext4_filename *fname, memset(de, 0, len); /* wipe old data */ de = (struct ext4_dir_entry_2 *) data2; top = data2 + len; - while ((char *)(de2 = ext4_next_entry(de, blocksize)) < top) + while ((char *)(de2 = ext4_next_entry(de, blocksize)) < top) { + if (ext4_check_dir_entry(dir, NULL, de, bh2, data2, len, + (data2 + (blocksize - csum_size) - + (char *) de))) { + brelse(bh2); + brelse(bh); + return -EFSCORRUPTED; + } de = de2; + } de->rec_len = ext4_rec_len_to_disk(data2 + (blocksize - csum_size) - (char *) de, blocksize);
