Changing size of a file on server and local update (fuse_write_update_size)
should be always protected by inode->i_mutex. Otherwise a race like this is
possible:
1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE).
fuse_file_fallocate() sends FUSE_FALLOCATE request to the server.
2. Process 'B' performs ordinary buffered write(2) with a length big enough
to extend the file beyond "offset + length" of fallocate call.
3. Process 'A' resumes execution of fuse_file_fallocate() and calls
fuse_write_update_size(inode, offset + length). But 'offset + length' was
obsoleted by write from previous step.
Signed-off-by: Maxim V. Patlasov <mpatla...@parallels.com>
---
fs/fuse/file.c | 10 ++++++----
1 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index e570081..8dfbf7d 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2470,14 +2470,16 @@ static long fuse_file_fallocate(struct file *file, int
mode, loff_t offset,
.mode = mode
};
int err;
+ bool lock_inode = !(mode & FALLOC_FL_KEEP_SIZE) ||
+ (mode & FALLOC_FL_PUNCH_HOLE);
if (fc->no_fallocate)
return -EOPNOTSUPP;
- if (mode & FALLOC_FL_PUNCH_HOLE) {
+ if (lock_inode)
mutex_lock(&inode->i_mutex);
+ if (mode & FALLOC_FL_PUNCH_HOLE)
fuse_set_nowrite(inode);
- }
req = fuse_get_req_nopages(fc);
if (IS_ERR(req)) {
@@ -2511,10 +2513,10 @@ static long fuse_file_fallocate(struct file *file, int
mode, loff_t offset,
fuse_invalidate_attr(inode);
out:
- if (mode & FALLOC_FL_PUNCH_HOLE) {
+ if (mode & FALLOC_FL_PUNCH_HOLE)
fuse_release_nowrite(inode);
+ if (lock_inode)
mutex_unlock(&inode->i_mutex);
- }
return err;
}
--
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