From 09ebb17ab476b6ac1cc07b53d07e88f4d31ee4d3 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 18 Feb 2014 12:00:21 +0100 Subject: udf: Fix data corruption on file type conversion UDF has two types of files - files with data stored in inode (ICB in UDF terminology) and files with data stored in external data blocks. We convert file from in-inode format to external format in udf_file_aio_write() when we find out data won't fit into inode any longer. However the following race between two O_APPEND writes can happen: CPU1 CPU2 udf_file_aio_write() udf_file_aio_write() down_write(&iinfo->i_data_sem); checks that i_size + count1 fits within inode => no need to convert up_write(&iinfo->i_data_sem); down_write(&iinfo->i_data_sem); checks that i_size + count2 fits within inode => no need to convert up_write(&iinfo->i_data_sem); generic_file_aio_write() - extends file by count1 bytes generic_file_aio_write() - extends file by count2 bytes Clearly if count1 + count2 doesn't fit into the inode, we overwrite kernel buffers beyond inode, possibly corrupting the filesystem as well. Fix the problem by acquiring i_mutex before checking whether write fits into the inode and using __generic_file_aio_write() afterwards which puts check and write into one critical section. Reported-by: Al Viro Signed-off-by: Jan Kara --- fs/udf/inode.c | 1 + 1 file changed, 1 insertion(+) (limited to 'fs/udf/inode.c') diff --git a/fs/udf/inode.c b/fs/udf/inode.c index 062b7925bca0..982ce05c87ed 100644 --- a/fs/udf/inode.c +++ b/fs/udf/inode.c @@ -265,6 +265,7 @@ int udf_expand_file_adinicb(struct inode *inode) .nr_to_write = 1, }; + WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex)); if (!iinfo->i_lenAlloc) { if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_SHORT_AD)) iinfo->i_alloc_type = ICBTAG_FLAG_AD_SHORT; -- cgit v1.2.3