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

Miklos Szeredi
2008-04-25T17:57:00Z

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From: Miklos Szeredi <mszeredi@suse.cz>

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@suse.cz>
---
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,

--