linux-ext4 - [PATCH] ext4: limit xattr size to INT

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Date:   Thu, 29 Mar 2018 17:46:39 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     adilger@...ger.ca, ebiggers3@...il.com, wen.xu@...ech.edu,
        ebiggers@...gle.com, Theodore Ts'o <tytso@....edu>,
        stable@...r.kernel.org
Subject: [PATCH] ext4: limit xattr size to INT_MAX

From: Eric Biggers <ebiggers@...gle.com>

ext4 isn't validating the sizes of xattrs.  This is problematic
because ->e_value_size is a u32, but ext4_xattr_get() returns an int.
A very large size is misinterpreted as an error code, which
ext4_get_acl() translates into a bogus ERR_PTR() for which IS_ERR()
returns false, causing a crash.

Fix this by validating that all xattrs are <= INT_MAX bytes.  Also add
explicit checks in ext4_xattr_block_get() and ext4_xattr_ibody_get()
just in case the xattr block is corrupted in memory.

This issue has been assigned CVE-2018-1095.

https://bugzilla.kernel.org/show_bug.cgi?id=199185
https://bugzilla.redhat.com/show_bug.cgi?id=1560793

Reported-by: Wen Xu <wen.xu@...ech.edu>
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Cc: stable@...r.kernel.org
---
 fs/ext4/xattr.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 63656dbafdc4..fea1108c3bea 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -201,6 +201,9 @@ ext4_xattr_check_entries(struct ext4_xattr_entry *entry, void *end,
 			u32 size = le32_to_cpu(entry->e_value_size);
 			void *value;
 
+			if (size > INT_MAX)
+				return -EFSCORRUPTED;
+
 			/*
 			 * The value cannot overlap the names, and the value
 			 * with padding cannot extend beyond 'end'.  Check both
@@ -523,8 +526,10 @@ ext4_xattr_block_get(struct inode *inode, int name_index, const char *name,
 	if (error)
 		goto cleanup;
 	size = le32_to_cpu(entry->e_value_size);
+	error = -ERANGE;
+	if (unlikely(size > INT_MAX))
+		goto cleanup;
 	if (buffer) {
-		error = -ERANGE;
 		if (size > buffer_size)
 			goto cleanup;
 		if (entry->e_value_inum) {
@@ -572,8 +577,10 @@ ext4_xattr_ibody_get(struct inode *inode, int name_index, const char *name,
 	if (error)
 		goto cleanup;
 	size = le32_to_cpu(entry->e_value_size);
+	error = -ERANGE;
+	if (unlikely(size > INT_MAX))
+		goto cleanup;
 	if (buffer) {
-		error = -ERANGE;
 		if (size > buffer_size)
 			goto cleanup;
 		if (entry->e_value_inum) {
-- 
2.16.1.72.g5be1f00a9a