Backport security fixe to 4.9 and 4.4 stable trees

Due to lack of proper validation that cached inodes are free during allocation, causes a crash (refer to CVE-2018-13093 for more details). To address this issue, I'm backporting upstream commit [1] to 4.4 and 4.9 stable trees (a backport of [1] to 4.14 already exists).

Also, commit [1] references another commit [2] which added checks only to xfs_iget_cache_miss(). In this patch, those checks have been moved into a dedicated checker method and both xfs_iget_cache_miss() and xfs_iget_cache_hit() are made to call that method. This code reorg in commit [1], makes commit [2] redundant in the history of the 4.9 and 4.4 stable trees. So commit [2] is not being backported.

-- Sid

[1]: afca6c5b2595f ("xfs: validate cached inodes are free when allocated") [2]: ee457001ed6c ("xfs: catch inode allocation state mismatch corruption")

[v4.9]
Dave Chinner (1):
xfs: More robust inode extent count validation

 fs/xfs/libxfs/xfs_format.h    |   3 ++
 fs/xfs/libxfs/xfs_inode_buf.c | 112 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 112 insertions(+), 3 deletions(-)

[v.4.4]
Dave Chinner (1):
xfs: validate cached inodes are free when allocated

 fs/xfs/xfs_icache.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 50 insertions(+), 7 deletions(-)

2.7.4

From: Dave Chinner <[email protected]>

commit afca6c5b2595fc44383919fba740c194b0b76aff upstream.

A recent fuzzed filesystem image cached random dcache corruption when the reproducer was run. This often showed up as panics in lookup_slow() on a null inode->i_ops pointer when doing pathwalks.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
....
Call Trace:
 lookup_slow+0x44/0x60
 walk_component+0x3dd/0x9f0
 link_path_walk+0x4a7/0x830
 path_lookupat+0xc1/0x470
 filename_lookup+0x129/0x270
 user_path_at_empty+0x36/0x40
 path_listxattr+0x98/0x110
 SyS_listxattr+0x13/0x20
 do_syscall_64+0xf5/0x280
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

but had many different failure modes including deadlocks trying to lock the inode that was just allocated or KASAN reports of use-after-free violations.

The cause of the problem was a corrupt INOBT on a v4 fs where the root inode was marked as free in the inobt record. Hence when we allocated an inode, it chose the root inode to allocate, found it in the cache and re-initialised it.

We recently fixed a similar inode allocation issue caused by inobt record corruption problem in xfs_iget_cache_miss() in commit ee457001ed6c ("xfs: catch inode allocation state mismatch corruption"). This change adds similar checks to the cache-hit path to catch it, and turns the reproducer into a corruption shutdown situation.

---
 fs/xfs/xfs_icache.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 50 insertions(+), 7 deletions(-)

index adbc1f5..7efeefb 100644
@@ -135,6 +135,46 @@ xfs_inode_free(
 }
 
 /*
+ * If we are allocating a new inode, then check what was returned is
+ * actually a free, empty inode. If we are not allocating an inode,
+ * then check we didn't find a free inode.
+ *
+ * Returns:
+ *	0		if the inode free state matches the lookup context
+ *	-ENOENT		if the inode is free and we are not allocating
+ *	-EFSCORRUPTED	if there is any state mismatch at all
+ */
+static int
+xfs_iget_check_free_state(
+	struct xfs_inode	*ip,
+	int			flags)
+{
+	if (flags & XFS_IGET_CREATE) {
+		/* should be a free inode */
+		if (VFS_I(ip)->i_mode != 0) {
+			xfs_warn(ip->i_mount,
+"Corruption detected! Free inode 0x%llx not marked free! (mode 0x%x)",
+				ip->i_ino, VFS_I(ip)->i_mode);
+			return -EFSCORRUPTED;
+		}
+
+		if (ip->i_d.di_nblocks != 0) {
+			xfs_warn(ip->i_mount,
+"Corruption detected! Free inode 0x%llx has blocks allocated!",
+				ip->i_ino);
+			return -EFSCORRUPTED;
+		}
+		return 0;
+	}
+
+	/* should be an allocated inode */
+	if (VFS_I(ip)->i_mode == 0)
+		return -ENOENT;
+
+	return 0;
+}
+
+/*
  * Check the validity of the inode we just found it the cache
  */
 static int

@@ -183,12 +223,12 @@ xfs_iget_cache_hit(
 	}
 
 	/*
-	 * If lookup is racing with unlink return an error immediately.
+	 * Check the inode free state is valid. This also detects lookup
+	 * racing with unlinks.
 	 */
-	if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {
-		error = -ENOENT;
+	error = xfs_iget_check_free_state(ip, flags);
+	if (error)
 		goto out_error;
-	}
 
 	/*
 	 * If IRECLAIMABLE is set, we've torn down the VFS inode already.

@@ -298,10 +338,13 @@ xfs_iget_cache_miss(
 
 	trace_xfs_iget_miss(ip);
 
-	if ((ip->i_d.di_mode == 0) && !(flags & XFS_IGET_CREATE)) {
-		error = -ENOENT;
+	/*
+	 * Check the inode free state is valid. This also detects lookup
+	 * racing with unlinks.
+	 */
+	error = xfs_iget_check_free_state(ip, flags);
+	if (error)
 		goto out_destroy;
-	}
 
 	/*
 	 * Preload the radix tree so we can insert safely under the

2.7.4

From: Dave Chinner <[email protected]>

commit 23fcb3340d033d9f081e21e6c12c2db7eaa541d3 upstream.

When the inode is in extent format, it can't have more extents that fit in the inode fork. We don't currenty check this, and so this corruption goes unnoticed by the inode verifiers. This can lead to crashes operating on invalid in-memory structures.

Attempts to access such a inode will now error out in the verifier rather than allowing modification operations to proceed.

---
 fs/xfs/libxfs/xfs_format.h    |   3 ++
 fs/xfs/libxfs/xfs_inode_buf.c | 112 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 112 insertions(+), 3 deletions(-)

index 6b7579e..9967d30 100644
@@ -979,6 +979,9 @@ typedef enum xfs_dinode_fmt {
 		XFS_DFORK_DSIZE(dip, mp) : \
 		XFS_DFORK_ASIZE(dip, mp))
 
+#define XFS_DFORK_MAXEXT(dip, mp, w) \
+	(XFS_DFORK_SIZE(dip, mp, w) / sizeof(struct xfs_bmbt_rec))
+
 /*
  * Return pointers to the data or attribute forks.
  */

2.7.4

Please ignore this patch set, I accidentally added another patch I was working on. Will send v2 with the right patches.

Thanks!

-- Sid.

What patch set? I see nothing in this email, so I have no idea what you are referring to :(

greg k-h

Apologies! Looks like my email thread was broken. I was referring to the thread here: https://lkml.org/lkml/2020/5/14/1326 with subject:

"[PATCH] Backport security fixe to 4.9 and 4.4 stable trees"

The corrected version (v2) of this patch should have reached you (hopefully) with the subject:

"[PATCH v2] Backport xfs security fix to 4.9 and 4.4 stable trees"

Thanks!

-- Sid.

Sorry, I see no such email in my staging patch queue.

Do you have a link to the series on lore.kernel.org? lkml.org is a mess and not under our control.

greg k-h

That's because it Cc'd [email protected] and not [email protected].

Should Siddharth resend?

-- Steve

Yes, [email protected] is a direct path to /dev/null on the kernel.org mail server.

thanks,

greg k-h