[patch 3/5] fuse: fix race in llseek

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@xxxxxxx>

Fuse doesn't use i_mutex to protect setting i_size, and so
generic_file_llseek() can be racy: it doesn't use i_size_read().

So do a fuse specific llseek method, which does use i_size_read().

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
 fs/fuse/file.c |   29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

Index: linux/fs/fuse/file.c
===================================================================
--- linux.orig/fs/fuse/file.c	2008-04-25 19:38:10.000000000 +0200
+++ linux/fs/fuse/file.c	2008-04-25 19:40:11.000000000 +0200
@@ -1425,8 +1425,33 @@ static sector_t fuse_bmap(struct address
 	return err ? 0 : outarg.block;
 }
 
+static loff_t fuse_file_llseek(struct file *file, loff_t offset, int origin)
+{
+	long long retval;
+	struct inode *inode = file->f_path.dentry->d_inode;
+
+	mutex_lock(&inode->i_mutex);
+	switch (origin) {
+	case SEEK_END:
+		offset += i_size_read(inode);
+		break;
+	case SEEK_CUR:
+		offset += file->f_pos;
+	}
+	retval = -EINVAL;
+	if (offset >= 0 && offset <= inode->i_sb->s_maxbytes) {
+		if (offset != file->f_pos) {
+			file->f_pos = offset;
+			file->f_version = 0;
+		}
+		retval = offset;
+	}
+	mutex_unlock(&inode->i_mutex);
+	return retval;
+}
+
 static const struct file_operations fuse_file_operations = {
-	.llseek		= generic_file_llseek,
+	.llseek		= fuse_file_llseek,
 	.read		= do_sync_read,
 	.aio_read	= fuse_file_aio_read,
 	.write		= do_sync_write,
@@ -1442,7 +1467,7 @@ static const struct file_operations fuse
 };
 
 static const struct file_operations fuse_direct_io_file_operations = {
-	.llseek		= generic_file_llseek,
+	.llseek		= fuse_file_llseek,
 	.read		= fuse_direct_read,
 	.write		= fuse_direct_write,
 	.open		= fuse_open,

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