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fuse: fix uninit-value in fuse_dentry_revalidate() 

fuse_dentry_revalidate() may be called with a dentry that didn't had
->d_time initialised.  The issue was found with KMSAN, where lookup_open()
calls __d_alloc(), followed by d_revalidate(), as shown below:

=====================================================
BUG: KMSAN: uninit-value in fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
 d_revalidate fs/namei.c:1030 [inline]
 lookup_open fs/namei.c:4405 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x1614/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859
[...]

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4466 [inline]
 slab_alloc_node mm/slub.c:4788 [inline]
 kmem_cache_alloc_lru_noprof+0x382/0x1280 mm/slub.c:4807
 __d_alloc+0x55/0xa00 fs/dcache.c:1740
 d_alloc_parallel+0x99/0x2740 fs/dcache.c:2604
 lookup_open fs/namei.c:4398 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0x135f/0x64c0 fs/namei.c:4827
 do_file_open+0x2aa/0x680 fs/namei.c:4859
[...]
=====================================================

Reported-by: syzbot+fdebb2dc960aa56c600a@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/69917e0d.050a0220.340abe.02e2.GAE@google.com
Fixes: 2396356a94 ("fuse: add more control over cache invalidation behaviour")
Signed-off-by: Luis Henriques <luis@igalia.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
master
Luis Henriques 2026-02-16 14:48:30 +00:00 committed by Miklos Szeredi
parent 8d306cbffc
commit 5a6baf2046
1 changed files with 5 additions and 0 deletions
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5
fs/fuse/dir.c
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@ -480,6 +480,11 @@ static int fuse_dentry_init(struct dentry *dentry)
fd->dentry = dentry;
RB_CLEAR_NODE(&fd->node);
dentry->d_fsdata = fd;
/*
* Initialising d_time (epoch) to '0' ensures the dentry is invalid
* if compared to fc->epoch, which is initialized to '1'.
*/
dentry->d_time = 0;
return 0;
}