Syzbot reported an issue with ext4 extents. The reproducer creates a corrupted ext4 fs image in memory, and mounts it as a loop device. It invokes the ext4_cache_extents() and ext4_find_extent(), which eventually triggers a BUG() in ext4_es_end() causing a kernel crash. It triggers on mainline, and every kernel version back to v4.14. Add a call ext4_ext_check_inode() in ext4_find_extent() to prevent the crash.
To: "Theodore Ts'o" tytso@mit.edu Cc: "Andreas Dilger" adilger.kernel@dilger.ca Cc: linux-ext4@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org
Link: https://syzkaller.appspot.com/bug?id=641e7a4b900015c5d7a729d6cc1fba7a928a88f... Reported-by: syzbot+a22dc4b0744ac658ed9b@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struk tadeusz.struk@linaro.org --- fs/ext4/extents.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 5235974126bd..c7b5a11e1abc 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -897,6 +897,12 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block, goto err; }
+ ret = ext4_ext_check_inode(inode); + if (ret) { + EXT4_ERROR_INODE(inode, "inode has invalid extent"); + goto err; + } + if (path) { ext4_ext_drop_refs(path); if (depth > path[0].p_maxdepth) {
On 9/30/22 13:25, Tadeusz Struk wrote:
Syzbot reported an issue with ext4 extents. The reproducer creates a corrupted ext4 fs image in memory, and mounts it as a loop device. It invokes the ext4_cache_extents() and ext4_find_extent(), which eventually triggers a BUG() in ext4_es_end() causing a kernel crash. It triggers on mainline, and every kernel version back to v4.14. Add a call ext4_ext_check_inode() in ext4_find_extent() to prevent the crash.
To: "Theodore Ts'o"tytso@mit.edu Cc: "Andreas Dilger"adilger.kernel@dilger.ca Cc:linux-ext4@vger.kernel.org Cc:linux-kernel@vger.kernel.org Cc:stable@vger.kernel.org
Link:https://syzkaller.appspot.com/bug?id=641e7a4b900015c5d7a729d6cc1fba7a928a88f... Reported-by:syzbot+a22dc4b0744ac658ed9b@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struktadeusz.struk@linaro.org
Hi, Any comments/feedback on this one?
On Tue, Oct 11, 2022 at 11:38:37AM -0700, Tadeusz Struk wrote:
On 9/30/22 13:25, Tadeusz Struk wrote:
Syzbot reported an issue with ext4 extents. The reproducer creates a corrupted ext4 fs image in memory, and mounts it as a loop device. It invokes the ext4_cache_extents() and ext4_find_extent(), which eventually triggers a BUG() in ext4_es_end() causing a kernel crash. It triggers on mainline, and every kernel version back to v4.14. Add a call ext4_ext_check_inode() in ext4_find_extent() to prevent the crash.
To: "Theodore Ts'o"tytso@mit.edu Cc: "Andreas Dilger"adilger.kernel@dilger.ca Cc:linux-ext4@vger.kernel.org Cc:linux-kernel@vger.kernel.org Cc:stable@vger.kernel.org
Link:https://syzkaller.appspot.com/bug?id=641e7a4b900015c5d7a729d6cc1fba7a928a88f... Reported-by:syzbot+a22dc4b0744ac658ed9b@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struktadeusz.struk@linaro.org
Any comments/feedback on this one?
Hi, I can't replicate the problem using the syzkaller repro:
root@kvm-xfstests:/vdc# /vtmp/repro [ 14.840406] loop0: detected capacity change from 0 to 1051 [ 14.840965] EXT4-fs (loop0): ext4_check_descriptors: Checksum for group 0 failed (60935!=0) [ 14.841468] EXT4-fs error (device loop0): ext4_ext_check_inode:520: inode #2: comm repro: pblk 0 bad header/extent: invalid magic - magic 9fe4, entries 42, max 0(0), depth 0(0) [ 14.842188] EXT4-fs (loop0): get root inode failed [ 14.842401] EXT4-fs (loop0): mount failed
And by inspection, if there is a corrupted inode, it should have been caught much sooner, in ext4_iget():
} else if (!ext4_has_inline_data(inode)) { /* validate the block references in the inode */ if (!(EXT4_SB(sb)->s_mount_state & EXT4_FC_REPLAY) && (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) || (S_ISLNK(inode->i_mode) && !ext4_inode_is_fast_symlink(inode)))) { if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) ret = ext4_ext_check_inode(inode); else ret = ext4_ind_check_inode(inode); } } if (ret) goto bad_inode;
... and this check has been around for quite some time.
It's much more efficient to check for a corrupted inode data structure at the time when the inode is read into memory, as opposed to every single time we try to lookup a logical->physical block map, in ext4_find_extent().
If you can reproduce a failure on a modern kernel, please let me know, but it looks like syzkaller had only reported it on androd-54, android-5-10, linux-4.14, and linux-4.19 in any case.
Cheers,
- Ted
linux-stable-mirror@lists.linaro.org
-
Tadeusz Struk -
Theodore Ts'o