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Message-Id: <20221011155745.15264-1-lhenriques@suse.de>
Date: Tue, 11 Oct 2022 16:57:45 +0100
From: Luís Henriques <lhenriques@...e.de>
To: "Theodore Ts'o" <tytso@....edu>,
Andreas Dilger <adilger.kernel@...ger.ca>
Cc: linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
Luís Henriques <lhenriques@...e.de>,
stable@...r.kernel.org
Subject: [PATCH] ext4: fix BUG_ON() when a directory entry has an invalid rec_len
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_ON() 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
This fix simply returns -EFSCORRUPTED when this happens.
CC: stable@...r.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216540
Signed-off-by: Luís Henriques <lhenriques@...e.de>
---
fs/ext4/namei.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 3a31b662f661..06803292e394 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2254,8 +2254,18 @@ 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 (de->rec_len & 3) {
+ EXT4_ERROR_INODE(
+ dir,
+ "rec_len for '..' not multiple of 4 (%u)",
+ de->rec_len);
+ brelse(bh2);
+ brelse(bh);
+ return -EFSCORRUPTED;
+ }
de = de2;
+ }
de->rec_len = ext4_rec_len_to_disk(data2 + (blocksize - csum_size) -
(char *) de, blocksize);
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