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 <viro@ZenIV.linux.org.uk>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/file.c b/fs/udf/file.c
index c02a27a..1037637 100644
--- a/fs/udf/file.c
+++ b/fs/udf/file.c
@@ -144,6 +144,7 @@
size_t count = iocb->ki_nbytes;
struct udf_inode_info *iinfo = UDF_I(inode);
+ mutex_lock(&inode->i_mutex);
down_write(&iinfo->i_data_sem);
if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
if (file->f_flags & O_APPEND)
@@ -156,6 +157,7 @@
pos + count)) {
err = udf_expand_file_adinicb(inode);
if (err) {
+ mutex_unlock(&inode->i_mutex);
udf_debug("udf_expand_adinicb: err=%d\n", err);
return err;
}
@@ -169,9 +171,17 @@
} else
up_write(&iinfo->i_data_sem);
- retval = generic_file_aio_write(iocb, iov, nr_segs, ppos);
- if (retval > 0)
+ retval = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
+ mutex_unlock(&inode->i_mutex);
+
+ if (retval > 0) {
+ ssize_t err;
+
mark_inode_dirty(inode);
+ err = generic_write_sync(file, iocb->ki_pos - retval, retval);
+ if (err < 0)
+ retval = err;
+ }
return retval;
}