syzbot reported a use-after-free Read in ext4_find_extent that is hit when using a corrupted file system. The bug was reported on Android 5.15, but using the same reproducer triggers the bug on v6.2-rc1 as well.
Fix the use-after-free by checking the extent header magic. An alternative would be to check the values of EXT4_{FIRST,LAST}_{EXTENT,INDEX} used in ext4_ext_binsearch() and ext4_ext_binsearch_idx(), so that we make sure that pointers returned by EXT4_{FIRST,LAST}_{EXTENT,INDEX} don't exceed the bounds of the extent tree node. But this alternative will not squash the bug for the cases where eh->eh_entries fit into eh->eh_max. We could also try to check the sanity of the path, but costs more than checking just the header magic, so stick to the header magic sanity check.
Link: https://syzkaller.appspot.com/bug?id=be6e90ce70987950e6deb3bac8418344ca8b96c... Reported-by: syzbot+0827b4b52b5ebf65f219@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Tudor Ambarus tudor.ambarus@linaro.org --- v2: drop wrong/uneeded le16_to_cpu() conversion for eh->eh_magic
fs/ext4/extents.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 9de1c9d1a13d..bedc8c098449 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -894,6 +894,12 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block, gfp_flags |= __GFP_NOFAIL;
eh = ext_inode_hdr(inode); + if (eh->eh_magic != EXT4_EXT_MAGIC) { + EXT4_ERROR_INODE(inode, "Extent header has invalid magic."); + ret = -EFSCORRUPTED; + goto err; + } + depth = ext_depth(inode); if (depth < 0 || depth > EXT4_MAX_EXTENT_DEPTH) { EXT4_ERROR_INODE(inode, "inode has invalid extent depth: %d",