From a818101d7b92e76db2f9a597e4830734767473b9 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 9 Aug 2016 17:41:16 +0100 Subject: [PATCH] cachefiles: Fix attempt to read i_blocks after deleting file [ver #2] An NULL-pointer dereference happens in cachefiles_mark_object_inactive() when it tries to read i_blocks so that it can tell the cachefilesd daemon how much space it's making available. The problem is that cachefiles_drop_object() calls cachefiles_mark_object_inactive() after calling cachefiles_delete_object() because the object being marked active staves off attempts to (re-)use the file at that filename until after it has been deleted. This means that d_inode is NULL by the time we come to try to access it. To fix the problem, have the caller of cachefiles_mark_object_inactive() supply the number of blocks freed up. Without this, the following oops may occur: BUG: unable to handle kernel NULL pointer dereference at 0000000000000098 IP: [] cachefiles_mark_object_inactive+0x61/0xb0 [cachefiles] ... CPU: 11 PID: 527 Comm: kworker/u64:4 Tainted: G I ------------ 3.10.0-470.el7.x86_64 #1 Hardware name: Hewlett-Packard HP Z600 Workstation/0B54h, BIOS 786G4 v03.19 03/11/2011 Workqueue: fscache_object fscache_object_work_func [fscache] task: ffff880035edaf10 ti: ffff8800b77c0000 task.ti: ffff8800b77c0000 RIP: 0010:[] cachefiles_mark_object_inactive+0x61/0xb0 [cachefiles] RSP: 0018:ffff8800b77c3d70 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff8800bf6cc400 RCX: 0000000000000034 RDX: 0000000000000000 RSI: ffff880090ffc710 RDI: ffff8800bf761ef8 RBP: ffff8800b77c3d88 R08: 2000000000000000 R09: 0090ffc710000000 R10: ff51005d2ff1c400 R11: 0000000000000000 R12: ffff880090ffc600 R13: ffff8800bf6cc520 R14: ffff8800bf6cc400 R15: ffff8800bf6cc498 FS: 0000000000000000(0000) GS:ffff8800bb8c0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 0000000000000098 CR3: 00000000019ba000 CR4: 00000000000007e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Stack: ffff880090ffc600 ffff8800bf6cc400 ffff8800867df140 ffff8800b77c3db0 ffffffffa06c48cb ffff880090ffc600 ffff880090ffc180 ffff880090ffc658 ffff8800b77c3df0 ffffffffa085d846 ffff8800a96b8150 ffff880090ffc600 Call Trace: [] cachefiles_drop_object+0x6b/0xf0 [cachefiles] [] fscache_drop_object+0xd6/0x1e0 [fscache] [] fscache_object_work_func+0xa5/0x200 [fscache] [] process_one_work+0x17b/0x470 [] worker_thread+0x126/0x410 [] ? rescuer_thread+0x460/0x460 [] kthread+0xcf/0xe0 [] ? kthread_create_on_node+0x140/0x140 [] ret_from_fork+0x58/0x90 [] ? kthread_create_on_node+0x140/0x140 The oopsing code shows: callq 0xffffffff810af6a0 mov 0xf8(%r12),%rax mov 0x30(%rax),%rax mov 0x98(%rax),%rax <---- oops here lock add %rax,0x130(%rbx) where this is: d_backing_inode(object->dentry)->i_blocks Fixes: a5b3a80b899bda0f456f1246c4c5a1191ea01519 (CacheFiles: Provide read-and-reset release counters for cachefilesd) Reported-by: Jianhong Yin Signed-off-by: David Howells Reviewed-by: Jeff Layton Reviewed-by: Steve Dickson cc: stable@vger.kernel.org Signed-off-by: Al Viro --- fs/cachefiles/interface.c | 8 +++++++- fs/cachefiles/internal.h | 3 ++- fs/cachefiles/namei.c | 8 ++++---- 3 files changed, 13 insertions(+), 6 deletions(-) diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c index ce5f345..e7f16a7 100644 --- a/fs/cachefiles/interface.c +++ b/fs/cachefiles/interface.c @@ -253,6 +253,8 @@ static void cachefiles_drop_object(struct fscache_object *_object) struct cachefiles_object *object; struct cachefiles_cache *cache; const struct cred *saved_cred; + struct inode *inode; + blkcnt_t i_blocks = 0; ASSERT(_object); @@ -279,6 +281,10 @@ static void cachefiles_drop_object(struct fscache_object *_object) _object != cache->cache.fsdef ) { _debug("- retire object OBJ%x", object->fscache.debug_id); + inode = d_backing_inode(object->dentry); + if (inode) + i_blocks = inode->i_blocks; + cachefiles_begin_secure(cache, &saved_cred); cachefiles_delete_object(cache, object); cachefiles_end_secure(cache, saved_cred); @@ -292,7 +298,7 @@ static void cachefiles_drop_object(struct fscache_object *_object) /* note that the object is now inactive */ if (test_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags)) - cachefiles_mark_object_inactive(cache, object); + cachefiles_mark_object_inactive(cache, object, i_blocks); dput(object->dentry); object->dentry = NULL; diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h index 2fcde1a..cd1effe 100644 --- a/fs/cachefiles/internal.h +++ b/fs/cachefiles/internal.h @@ -160,7 +160,8 @@ extern char *cachefiles_cook_key(const u8 *raw, int keylen, uint8_t type); * namei.c */ extern void cachefiles_mark_object_inactive(struct cachefiles_cache *cache, - struct cachefiles_object *object); + struct cachefiles_object *object, + blkcnt_t i_blocks); extern int cachefiles_delete_object(struct cachefiles_cache *cache, struct cachefiles_object *object); extern int cachefiles_walk_to_object(struct cachefiles_object *parent, diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c index 3f7c2cd..c6ee4b5 100644 --- a/fs/cachefiles/namei.c +++ b/fs/cachefiles/namei.c @@ -261,10 +261,9 @@ requeue: * Mark an object as being inactive. */ void cachefiles_mark_object_inactive(struct cachefiles_cache *cache, - struct cachefiles_object *object) + struct cachefiles_object *object, + blkcnt_t i_blocks) { - blkcnt_t i_blocks = d_backing_inode(object->dentry)->i_blocks; - write_lock(&cache->active_lock); rb_erase(&object->active_node, &cache->active_nodes); clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags); @@ -707,7 +706,8 @@ mark_active_timed_out: check_error: _debug("check error %d", ret); - cachefiles_mark_object_inactive(cache, object); + cachefiles_mark_object_inactive( + cache, object, d_backing_inode(object->dentry)->i_blocks); release_dentry: dput(object->dentry); object->dentry = NULL; -- 2.7.4