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FAILED: patch "[PATCH] ovl: make ioctl() safe" failed to apply to 5.4-stable tree

PATCH [email protected] 1 participant 1 message Dec 28, 2020

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The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 89bdfaf93d9157499c3a0d61f489df66f2dead7f Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <[email protected]>
Date: Mon, 14 Dec 2020 15:26:14 +0100
Subject: [PATCH] ovl: make ioctl() safe

ovl_ioctl_set_flags() does a capability check using flags, but then the real ioctl double-fetches flags and uses potentially different value.

The "Check the capability before cred override" comment misleading: user can skip this check by presenting benign flags first and then overwriting them to non-benign flags.

Just remove the cred override for now, hoping this doesn't cause a regression.

The proper solution is to create a new setxflags i_op (patches are in the works).

Xfstests don't show a regression.

Reported-by Dmitry Vyukov <[email protected]>
Signed-off-by Miklos Szeredi <[email protected]>
Reviewed-by Amir Goldstein <[email protected]>
Fixes dab5ca8fd9dd ("ovl: add lsattr/chattr support")
Cc <[email protected]> # v4.19
fs/overlayfs/file.c +16 -71
index efccb7c1f9bc..a1f72ac053e5 100644
@@ -541,46 +541,31 @@ static long ovl_real_ioctl(struct file *file, unsigned int cmd,
 			   unsigned long arg)
 {
 	struct fd real;
-	const struct cred *old_cred;
 	long ret;
 
 	ret = ovl_real_fdget(file, &real);
 	if (ret)
 		return ret;
 
-	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = security_file_ioctl(real.file, cmd, arg);
-	if (!ret)
+	if (!ret) {
+		/*
+		 * Don't override creds, since we currently can't safely check
+		 * permissions before doing so.
+		 */
 		ret = vfs_ioctl(real.file, cmd, arg);
-	revert_creds(old_cred);
+	}
 
 	fdput(real);
 
 	return ret;
 }
 
-static unsigned int ovl_iflags_to_fsflags(unsigned int iflags)
-{
-	unsigned int flags = 0;
-
-	if (iflags & S_SYNC)
-		flags |= FS_SYNC_FL;
-	if (iflags & S_APPEND)
-		flags |= FS_APPEND_FL;
-	if (iflags & S_IMMUTABLE)
-		flags |= FS_IMMUTABLE_FL;
-	if (iflags & S_NOATIME)
-		flags |= FS_NOATIME_FL;
-
-	return flags;
-}
-
 static long ovl_ioctl_set_flags(struct file *file, unsigned int cmd,
-				unsigned long arg, unsigned int flags)
+				unsigned long arg)
 {
 	long ret;
 	struct inode *inode = file_inode(file);
-	unsigned int oldflags;
 
 	if (!inode_owner_or_capable(inode))
 		return -EACCES;

@@ -591,10 +576,13 @@ static long ovl_ioctl_set_flags(struct file *file, unsigned int cmd,
 
 	inode_lock(inode);
 
-	/* Check the capability before cred override */
-	oldflags = ovl_iflags_to_fsflags(READ_ONCE(inode->i_flags));
-	ret = vfs_ioc_setflags_prepare(inode, oldflags, flags);
-	if (ret)
+	/*
+	 * Prevent copy up if immutable and has no CAP_LINUX_IMMUTABLE
+	 * capability.
+	 */
+	ret = -EPERM;
+	if (!ovl_has_upperdata(inode) && IS_IMMUTABLE(inode) &&
+	    !capable(CAP_LINUX_IMMUTABLE))
 		goto unlock;
 
 	ret = ovl_maybe_copy_up(file_dentry(file), O_WRONLY);

@@ -613,46 +601,6 @@ static long ovl_ioctl_set_flags(struct file *file, unsigned int cmd,
 
 }
 
-static long ovl_ioctl_set_fsflags(struct file *file, unsigned int cmd,
-				  unsigned long arg)
-{
-	unsigned int flags;
-
-	if (get_user(flags, (int __user *) arg))
-		return -EFAULT;
-
-	return ovl_ioctl_set_flags(file, cmd, arg, flags);
-}
-
-static unsigned int ovl_fsxflags_to_fsflags(unsigned int xflags)
-{
-	unsigned int flags = 0;
-
-	if (xflags & FS_XFLAG_SYNC)
-		flags |= FS_SYNC_FL;
-	if (xflags & FS_XFLAG_APPEND)
-		flags |= FS_APPEND_FL;
-	if (xflags & FS_XFLAG_IMMUTABLE)
-		flags |= FS_IMMUTABLE_FL;
-	if (xflags & FS_XFLAG_NOATIME)
-		flags |= FS_NOATIME_FL;
-
-	return flags;
-}
-
-static long ovl_ioctl_set_fsxflags(struct file *file, unsigned int cmd,
-				   unsigned long arg)
-{
-	struct fsxattr fa;
-
-	memset(&fa, 0, sizeof(fa));
-	if (copy_from_user(&fa, (void __user *) arg, sizeof(fa)))
-		return -EFAULT;
-
-	return ovl_ioctl_set_flags(file, cmd, arg,
-				   ovl_fsxflags_to_fsflags(fa.fsx_xflags));
-}
-
 long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	long ret;

@@ -663,12 +611,9 @@ long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		ret = ovl_real_ioctl(file, cmd, arg);
 		break;
 
-	case FS_IOC_SETFLAGS:
-		ret = ovl_ioctl_set_fsflags(file, cmd, arg);
-		break;
-
 	case FS_IOC_FSSETXATTR:
-		ret = ovl_ioctl_set_fsxflags(file, cmd, arg);
+	case FS_IOC_SETFLAGS:
+		ret = ovl_ioctl_set_flags(file, cmd, arg);
 		break;
 
 	default: