[PATCH 1/2] ubifs: Fix races between xattr_{set|get} and listxattr operations

From: Zhihao Cheng
Date: Mon May 31 2021 - 08:43:13 EST

UBIFS may occur some problems with concurrent xattr_{set|get} and
listxattr operations, such as assertion failure, memory corruption,
stale xattr value[1].

Fix it by importing a new rw-lock in @ubifs_inode to serilize write
operations on xattr, concurrent read operations are still effective,
just like ext4.

[1] https://lore.kernel.org/linux-mtd/20200630130438.141649-1-houtao1@xxxxxxxxxx

Fixes: 1e51764a3c2ac05a23 ("UBIFS: add new flash file system")
Cc: stable@xxxxxxxxxxxxxxx # v2.6+
Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
---
fs/ubifs/super.c | 1 +
fs/ubifs/ubifs.h | 2 ++
fs/ubifs/xattr.c | 44 +++++++++++++++++++++++++++++++++-----------
3 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index f65f665c5e12..94cf4f4675fe 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -275,6 +275,7 @@ static struct inode *ubifs_alloc_inode(struct super_block *sb)
memset((void *)ui + sizeof(struct inode), 0,
sizeof(struct ubifs_inode) - sizeof(struct inode));
mutex_init(&ui->ui_mutex);
+ init_rwsem(&ui->xattr_sem);
spin_lock_init(&ui->ui_lock);
return &ui->vfs_inode;
};
diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h
index b65c599a386a..7e978f421430 100644
--- a/fs/ubifs/ubifs.h
+++ b/fs/ubifs/ubifs.h
@@ -356,6 +356,7 @@ struct ubifs_gced_idx_leb {
* @ui_mutex: serializes inode write-back with the rest of VFS operations,
* serializes "clean <-> dirty" state changes, serializes bulk-read,
* protects @dirty, @bulk_read, @ui_size, and @xattr_size
+ * @xattr_sem: serilizes write operations (remove|set|create) on xattr
* @ui_lock: protects @synced_i_size
* @synced_i_size: synchronized size of inode, i.e. the value of inode size
* currently stored on the flash; used only for regular file
@@ -409,6 +410,7 @@ struct ubifs_inode {
unsigned int bulk_read:1;
unsigned int compr_type:2;
struct mutex ui_mutex;
+ struct rw_semaphore xattr_sem;
spinlock_t ui_lock;
loff_t synced_i_size;
loff_t ui_size;
diff --git a/fs/ubifs/xattr.c b/fs/ubifs/xattr.c
index 6b1e9830b274..1fce27e9b769 100644
--- a/fs/ubifs/xattr.c
+++ b/fs/ubifs/xattr.c
@@ -285,6 +285,7 @@ int ubifs_xattr_set(struct inode *host, const char *name, const void *value,
if (!xent)
return -ENOMEM;

+ down_write(&ubifs_inode(host)->xattr_sem);
/*
* The extended attribute entries are stored in LNC, so multiple
* look-ups do not involve reading the flash.
@@ -319,6 +320,7 @@ int ubifs_xattr_set(struct inode *host, const char *name, const void *value,
iput(inode);

out_free:
+ up_write(&ubifs_inode(host)->xattr_sem);
kfree(xent);
return err;
}
@@ -341,18 +343,19 @@ ssize_t ubifs_xattr_get(struct inode *host, const char *name, void *buf,
if (!xent)
return -ENOMEM;

+ down_read(&ubifs_inode(host)->xattr_sem);
xent_key_init(c, &key, host->i_ino, &nm);
err = ubifs_tnc_lookup_nm(c, &key, xent, &nm);
if (err) {
if (err == -ENOENT)
err = -ENODATA;
- goto out_unlock;
+ goto out_cleanup;
}

inode = iget_xattr(c, le64_to_cpu(xent->inum));
if (IS_ERR(inode)) {
err = PTR_ERR(inode);
- goto out_unlock;
+ goto out_cleanup;
}

ui = ubifs_inode(inode);
@@ -374,7 +377,8 @@ ssize_t ubifs_xattr_get(struct inode *host, const char *name, void *buf,
out_iput:
mutex_unlock(&ui->ui_mutex);
iput(inode);
-out_unlock:
+out_cleanup:
+ up_read(&ubifs_inode(host)->xattr_sem);
kfree(xent);
return err;
}
@@ -406,16 +410,21 @@ ssize_t ubifs_listxattr(struct dentry *dentry, char *buffer, size_t size)
dbg_gen("ino %lu ('%pd'), buffer size %zd", host->i_ino,
dentry, size);

+ down_read(&host_ui->xattr_sem);
len = host_ui->xattr_names + host_ui->xattr_cnt;
- if (!buffer)
+ if (!buffer) {
/*
* We should return the minimum buffer size which will fit a
* null-terminated list of all the extended attribute names.
*/
- return len;
+ err = len;
+ goto out_err;
+ }

- if (len > size)
- return -ERANGE;
+ if (len > size) {
+ err = -ERANGE;
+ goto out_err;
+ }

lowest_xent_key(c, &key, host->i_ino);
while (1) {
@@ -437,8 +446,9 @@ ssize_t ubifs_listxattr(struct dentry *dentry, char *buffer, size_t size)
pxent = xent;
key_read(c, &xent->key, &key);
}
-
kfree(pxent);
+ up_read(&host_ui->xattr_sem);
+
if (err != -ENOENT) {
ubifs_err(c, "cannot find next direntry, error %d", err);
return err;
@@ -446,6 +456,10 @@ ssize_t ubifs_listxattr(struct dentry *dentry, char *buffer, size_t size)

ubifs_assert(c, written <= size);
return written;
+
+out_err:
+ up_read(&host_ui->xattr_sem);
+ return err;
}

static int remove_xattr(struct ubifs_info *c, struct inode *host,
@@ -504,6 +518,7 @@ int ubifs_purge_xattrs(struct inode *host)
ubifs_warn(c, "inode %lu has too many xattrs, doing a non-atomic deletion",
host->i_ino);

+ down_write(&ubifs_inode(host)->xattr_sem);
lowest_xent_key(c, &key, host->i_ino);
while (1) {
xent = ubifs_tnc_next_ent(c, &key, &nm);
@@ -523,7 +538,7 @@ int ubifs_purge_xattrs(struct inode *host)
ubifs_ro_mode(c, err);
kfree(pxent);
kfree(xent);
- return err;
+ goto out_err;
}

ubifs_assert(c, ubifs_inode(xino)->xattr);
@@ -535,7 +550,7 @@ int ubifs_purge_xattrs(struct inode *host)
kfree(xent);
iput(xino);
ubifs_err(c, "cannot remove xattr, error %d", err);
- return err;
+ goto out_err;
}

iput(xino);
@@ -544,14 +559,19 @@ int ubifs_purge_xattrs(struct inode *host)
pxent = xent;
key_read(c, &xent->key, &key);
}
-
kfree(pxent);
+ up_write(&ubifs_inode(host)->xattr_sem);
+
if (err != -ENOENT) {
ubifs_err(c, "cannot find next direntry, error %d", err);
return err;
}

return 0;
+
+out_err:
+ up_write(&ubifs_inode(host)->xattr_sem);
+ return err;
}

/**
@@ -594,6 +614,7 @@ static int ubifs_xattr_remove(struct inode *host, const char *name)
if (!xent)
return -ENOMEM;

+ down_write(&ubifs_inode(host)->xattr_sem);
xent_key_init(c, &key, host->i_ino, &nm);
err = ubifs_tnc_lookup_nm(c, &key, xent, &nm);
if (err) {
@@ -618,6 +639,7 @@ static int ubifs_xattr_remove(struct inode *host, const char *name)
iput(inode);

out_free:
+ up_write(&ubifs_inode(host)->xattr_sem);
kfree(xent);
return err;
}
--
2.25.4