linux-kernel - [PATCH 4.16 092/196] ext4: limit xattr size to INT

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Date:   Sun, 22 Apr 2018 15:51:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Wen Xu <wen.xu@...ech.edu>,
        Eric Biggers <ebiggers@...gle.com>,
        Theodore Tso <tytso@....edu>
Subject: [PATCH 4.16 092/196] ext4: limit xattr size to INT_MAX

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit ce3fd194fcc6fbdc00ce095a852f22df97baa401 upstream.

ext4 isn't validating the sizes of xattrs where the value of the xattr
is stored in an external inode.  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.

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
Fixes: e50e5129f384 ("ext4: xattr-in-inode support")
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/xattr.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -195,10 +195,13 @@ ext4_xattr_check_entries(struct ext4_xat
 
 	/* Check the values */
 	while (!IS_LAST_ENTRY(entry)) {
-		if (entry->e_value_size != 0 &&
-		    entry->e_value_inum == 0) {
+		u32 size = le32_to_cpu(entry->e_value_size);
+
+		if (size > INT_MAX)
+			return -EFSCORRUPTED;
+
+		if (size != 0 && entry->e_value_inum == 0) {
 			u16 offs = le16_to_cpu(entry->e_value_offs);
-			u32 size = le32_to_cpu(entry->e_value_size);
 			void *value;
 
 			/*