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cachefiles: Fix NULL pointer dereference in object->file

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At present, the object->file has the NULL pointer dereference problem in
ondemand-mode. The root cause is that the allocated fd and object->file
lifetime are inconsistent, and the user-space invocation to anon_fd uses
object->file. Following is the process that triggers the issue:

	  [write fd]				[umount]
cachefiles_ondemand_fd_write_iter
				       fscache_cookie_state_machine
					 cachefiles_withdraw_cookie
  if (!file) return -ENOBUFS
					   cachefiles_clean_up_object
					     cachefiles_unmark_inode_in_use
					     fput(object->file)
					     object->file = NULL
  // file NULL pointer dereference!
  __cachefiles_write(..., file, ...)

Fix this issue by add an additional reference count to the object->file
before write/llseek, and decrement after it finished.

Fixes: c838305450 ("cachefiles: notify the user daemon when looking up cookie")
Signed-off-by: Zizhi Wo <wozizhi@huawei.com>
Link: https://lore.kernel.org/r/20241107110649.3980193-5-wozizhi@huawei.com
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Zizhi Wo 2024-11-07 19:06:48 +08:00 committed by Christian Brauner
parent 09ecf8f550
commit 31ad74b202
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
2 changed files with 34 additions and 10 deletions
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12
fs/cachefiles/interface.c
View File

@ -327,6 +327,8 @@ static void cachefiles_commit_object(struct cachefiles_object *object,
static void cachefiles_clean_up_object(struct cachefiles_object *object,
struct cachefiles_cache *cache)
{
struct file *file;
if (test_bit(FSCACHE_COOKIE_RETIRED, &object->cookie->flags)) {
if (!test_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags)) {
cachefiles_see_object(object, cachefiles_obj_see_clean_delete);
@ -342,10 +344,14 @@ static void cachefiles_clean_up_object(struct cachefiles_object *object,
}
cachefiles_unmark_inode_in_use(object, object->file);
if (object->file) {
fput(object->file);
spin_lock(&object->lock);
file = object->file;
object->file = NULL;
}
spin_unlock(&object->lock);
if (file)
fput(file);
}
/*

30
fs/cachefiles/ondemand.c
View File

@ -60,20 +60,26 @@ static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb,
{
struct cachefiles_object *object = kiocb->ki_filp->private_data;
struct cachefiles_cache *cache = object->volume->cache;
struct file *file = object->file;
struct file *file;
size_t len = iter->count, aligned_len = len;
loff_t pos = kiocb->ki_pos;
const struct cred *saved_cred;
int ret;
if (!file)
spin_lock(&object->lock);
file = object->file;
if (!file) {
spin_unlock(&object->lock);
return -ENOBUFS;
}
get_file(file);
spin_unlock(&object->lock);
cachefiles_begin_secure(cache, &saved_cred);
ret = __cachefiles_prepare_write(object, file, &pos, &aligned_len, len, true);
cachefiles_end_secure(cache, saved_cred);
if (ret < 0)
return ret;
goto out;
trace_cachefiles_ondemand_fd_write(object, file_inode(file), pos, len);
ret = __cachefiles_write(object, file, pos, iter, NULL, NULL);
@ -82,6 +88,8 @@ static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb,
kiocb->ki_pos += ret;
}
out:
fput(file);
return ret;
}
@ -89,12 +97,22 @@ static loff_t cachefiles_ondemand_fd_llseek(struct file *filp, loff_t pos,
int whence)
{
struct cachefiles_object *object = filp->private_data;
struct file *file = object->file;
struct file *file;
loff_t ret;
if (!file)
spin_lock(&object->lock);
file = object->file;
if (!file) {
spin_unlock(&object->lock);
return -ENOBUFS;
}
get_file(file);
spin_unlock(&object->lock);
return vfs_llseek(file, pos, whence);
ret = vfs_llseek(file, pos, whence);
fput(file);
return ret;
}
static long cachefiles_ondemand_fd_ioctl(struct file *filp, unsigned int ioctl,