fs: Pass AT_GETATTR_NOSEC flag to getattr interface function

[ Upstream commit 8a924db2d7b5eb69ba08b1a0af46e9f1359a9bdf ]

When vfs_getattr_nosec() calls a filesystem's getattr interface function
then the 'nosec' should propagate into this function so that
vfs_getattr_nosec() can again be called from the filesystem's gettattr
rather than vfs_getattr(). The latter would add unnecessary security
checks that the initial vfs_getattr_nosec() call wanted to avoid.
Therefore, introduce the getattr flag GETATTR_NOSEC and allow to pass
with the new getattr_flags parameter to the getattr interface function.
In overlayfs and ecryptfs use this flag to determine which one of the
two functions to call.

In a recent code change introduced to IMA vfs_getattr_nosec() ended up
calling vfs_getattr() in overlayfs, which in turn called
security_inode_getattr() on an exiting process that did not have
current->fs set anymore, which then caused a kernel NULL pointer
dereference. With this change the call to security_inode_getattr() can
be avoided, thus avoiding the NULL pointer dereference.

Reported-by: <syzbot+a67fc5321ffb4b311c98@syzkaller.appspotmail.com>
Fixes: db1d1e8b9867 ("IMA: use vfs_getattr_nosec to get the i_version")
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <linux-fsdevel@vger.kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Tyler Hicks <code@tyhicks.com>
Cc: Mimi Zohar <zohar@linux.ibm.com>
Suggested-by: Christian Brauner <brauner@kernel.org>
Co-developed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Link: https://lore.kernel.org/r/20231002125733.1251467-1-stefanb@linux.vnet.ibm.com
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

2 files changed, 13 insertions, 5 deletions

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 83ef66644c21..fca29dba7b14 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -171,7 +171,7 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path,
 
 	type = ovl_path_real(dentry, &realpath);
 	old_cred = ovl_override_creds(dentry->d_sb);
-	err = vfs_getattr(&realpath, stat, request_mask, flags);
+	err = ovl_do_getattr(&realpath, stat, request_mask, flags);
 	if (err)
 		goto out;
 
@@ -196,8 +196,8 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path,
 					(!is_dir ? STATX_NLINK : 0);
 
 			ovl_path_lower(dentry, &realpath);
-			err = vfs_getattr(&realpath, &lowerstat,
-					  lowermask, flags);
+			err = ovl_do_getattr(&realpath, &lowerstat, lowermask,
+					     flags);
 			if (err)
 				goto out;
 
@@ -249,8 +249,8 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path,
 
 			ovl_path_lowerdata(dentry, &realpath);
 			if (realpath.dentry) {
-				err = vfs_getattr(&realpath, &lowerdatastat,
-						  lowermask, flags);
+				err = ovl_do_getattr(&realpath, &lowerdatastat,
+						     lowermask, flags);
 				if (err)
 					goto out;
 			} else {
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 9817b2dcb132..09ca82ed0f8c 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -397,6 +397,14 @@ static inline bool ovl_open_flags_need_copy_up(int flags)
 	return ((OPEN_FMODE(flags) & FMODE_WRITE) || (flags & O_TRUNC));
 }
 
+static inline int ovl_do_getattr(const struct path *path, struct kstat *stat,
+				 u32 request_mask, unsigned int flags)
+{
+	if (flags & AT_GETATTR_NOSEC)
+		return vfs_getattr_nosec(path, stat, request_mask, flags);
+	return vfs_getattr(path, stat, request_mask, flags);
+}
+
 /* util.c */
 int ovl_want_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);