fs/9p/xattr.c: catch the error of p9_client_clunk when setting xattr failed

In my testing, v9fs_fid_xattr_set will return successfully even if the backend ext4 filesystem has no space to store xattr key-value. That will cause inconsistent behavior between front end and back end. The reason is that lsetxattr will be triggered by p9_client_clunk, and unfortunately we did not catch the error. This patch will catch the error to notify upper caller.

p9_client_clunk (in 9p)
p9_client_rpc(clnt, P9_TCLUNK, "d", fid->fid);
v9fs_clunk (in qemu)
put_fid
free_fid
v9fs_xattr_fid_clunk
v9fs_co_lsetxattr
s->ops->lsetxattr
ext4_xattr_user_set (in host ext4 filesystem)

Signed-off-by Jun Piao <[email protected]>

---
 fs/9p/xattr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

fs/9p/xattr.c +1 -1

index f329eee..352abc3 100644
@@ -105,7 +105,7 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
 {
 	struct kvec kvec = {.iov_base = (void *)value, .iov_len = value_len};
 	struct iov_iter from;
-	int retval;
+	int retval, err;
 
 	iov_iter_kvec(&from, WRITE | ITER_KVEC, &kvec, 1, value_len);
 

fs/9p/xattr.c +3 -1

-	p9_client_clunk(fid);
+	err = p9_client_clunk(fid);
+	if (!retval && err)
+		retval = err;
 	return retval;
 }
 

piaojun wrote on Wed, Jul 25, 2018:

Quoted 17 lines

In my testing, v9fs_fid_xattr_set will return successfully even if the backend ext4 filesystem has no space to store xattr key-value. That will cause inconsistent behavior between front end and back end. The reason is that lsetxattr will be triggered by p9_client_clunk, and unfortunately we did not catch the error. This patch will catch the error to notify upper caller.

p9_client_clunk (in 9p)
p9_client_rpc(clnt, P9_TCLUNK, "d", fid->fid);
v9fs_clunk (in qemu)
put_fid
free_fid
v9fs_xattr_fid_clunk
v9fs_co_lsetxattr
s->ops->lsetxattr
ext4_xattr_user_set (in host ext4 filesystem)

Quoted 1 line

Signed-off-by Jun Piao <[email protected]>

Good catch!

LGTM on its own but see comment below for further error checking. Please let me know if you want to do this in a v2 or submit a separate patch altogether, I can pick this one up as it is.

Quoted 18 lines

---
 fs/9p/xattr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

fs/9p/xattr.c +1 -1

index f329eee..352abc3 100644
@@ -105,7 +105,7 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
 {
 	struct kvec kvec = {.iov_base = (void *)value, .iov_len = value_len};
 	struct iov_iter from;
-	int retval;
+	int retval, err;
 
 	iov_iter_kvec(&from, WRITE | ITER_KVEC, &kvec, 1, value_len);
 

fs/9p/xattr.c int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name, · line 128

Quoted 3 lines

fs/9p/xattr.c +0 -0

@@ -126,7 +126,9 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
 			 retval);
 	else
 		p9_client_write(fid, 0, &from, &retval);

I'm not sure what to do about this but it's also possible for p9_client_write to not write the full length without setting and error.

We should probably compare the return value of p9_client_write and value_len to detect short writes and return an error in this case.

fs/9p/xattr.c int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name, · line 134

Quoted 8 lines

fs/9p/xattr.c +3 -1

-	p9_client_clunk(fid);
+	err = p9_client_clunk(fid);
+	if (!retval && err)
+		retval = err;
 	return retval;
 }
 

.

Quoted 7 lines

Quoted 1 line

p9_client_write(fid, 0, &from, &retval);

I'm not sure what to do about this but it's also possible for p9_client_write to not write the full length without setting and error.

We should probably compare the return value of p9_client_write and value_len to detect short writes and return an error in this case.

It looks like we could identify short writes error from the *err. If no error case breaks the while loop, the total equal to the whole data len.