fuse: fix race in llseek

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().

[akpm@linux-foundation.org: make `retval' loff_t]
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 27 insertions, 2 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 2d3649e42599..9ced35b00686 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1431,8 +1431,33 @@ static sector_t fuse_bmap(struct address_space *mapping, sector_t block)
         return err ? 0 : outarg.block;
 }
 
+static loff_t fuse_file_llseek(struct file *file, loff_t offset, int origin)
+{
+        loff_t 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,
@@ -1448,7 +1473,7 @@ static const struct file_operations fuse_file_operations = {
 };
 
 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,