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authorHou Tao <houtao1@huawei.com>2021-09-28 22:07:50 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-09-28 18:18:15 +0200
commitdf38d852c6814cbbd010d81e84efb9dc057d5ba6 (patch)
treead383944792007504361434d095467499b3f33b9 /fs/kernfs
parentebd6823af378c7d91f80cbe83ce07b5f166744e4 (diff)
downloadlinux-df38d852c6814cbbd010d81e84efb9dc057d5ba6.tar.bz2
kernfs: also call kernfs_set_rev() for positive dentry
A KMSAN warning is reported by Alexander Potapenko: BUG: KMSAN: uninit-value in kernfs_dop_revalidate+0x61f/0x840 fs/kernfs/dir.c:1053 kernfs_dop_revalidate+0x61f/0x840 fs/kernfs/dir.c:1053 d_revalidate fs/namei.c:854 lookup_dcache fs/namei.c:1522 __lookup_hash+0x3a6/0x590 fs/namei.c:1543 filename_create+0x312/0x7c0 fs/namei.c:3657 do_mkdirat+0x103/0x930 fs/namei.c:3900 __do_sys_mkdir fs/namei.c:3931 __se_sys_mkdir fs/namei.c:3929 __x64_sys_mkdir+0xda/0x120 fs/namei.c:3929 do_syscall_x64 arch/x86/entry/common.c:51 It seems a positive dentry in kernfs becomes a negative dentry directly through d_delete() in vfs_rmdir(). dentry->d_time is uninitialized when accessing it in kernfs_dop_revalidate(), because it is only initialized when created as negative dentry in kernfs_iop_lookup(). The problem can be reproduced by the following command: cd /sys/fs/cgroup/pids && mkdir hi && stat hi && rmdir hi && stat hi A simple fixes seems to be initializing d->d_time for positive dentry in kernfs_iop_lookup() as well. The downside is the negative dentry will be revalidated again after it becomes negative in d_delete(), because the revison of its parent must have been increased due to its removal. Alternative solution is implement .d_iput for kernfs, and assign d_time for the newly-generated negative dentry in it. But we may need to take kernfs_rwsem to protect again the concurrent kernfs_link_sibling() on the parent directory, it is a little over-killing. Now the simple fix is chosen. Link: https://marc.info/?l=linux-fsdevel&m=163249838610499 Fixes: c7e7c04274b1 ("kernfs: use VFS negative dentry caching") Reported-by: Alexander Potapenko <glider@google.com> Signed-off-by: Hou Tao <houtao1@huawei.com> Link: https://lore.kernel.org/r/20210928140750.1274441-1-houtao1@huawei.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/kernfs')
-rw-r--r--fs/kernfs/dir.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index ba581429bf7b..cfc3ce8b815a 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1116,8 +1116,13 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
if (!inode)
inode = ERR_PTR(-ENOMEM);
}
- /* Needed only for negative dentry validation */
- if (!inode)
+ /*
+ * Needed for negative dentry validation.
+ * The negative dentry can be created in kernfs_iop_lookup()
+ * or transforms from positive dentry in dentry_unlink_inode()
+ * called from vfs_rmdir().
+ */
+ if (!IS_ERR(inode))
kernfs_set_rev(parent, dentry);
up_read(&kernfs_rwsem);