[PATCH 3.16 086/366] ext4: add extra checks to ext4_xattr_block_get()

Ben Hutchings
2018-10-14T23:23:50Z

From: Theodore Ts'o <tytso@mit.edu>

commit 54dd0e0a1b255f115f8647fc6fb93273251b01b9 upstream.

Add explicit checks in ext4_xattr_block_get() just in case the
e_value_offs and e_value_size fields in the the xattr block are
corrupted in memory after the buffer_verified bit is set on the xattr
block.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16:
- Drop change to ext4_xattr_check_entries() which is only needed for the
xattr-in-inode case
- Adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -327,12 +327,18 @@ bad_block:
if (error)
goto cleanup;
size = le32_to_cpu(entry->e_value_size);
+ error = -ERANGE;
+ if (unlikely(size > EXT4_XATTR_SIZE_MAX))
+ goto cleanup;
if (buffer) {
- error = -ERANGE;
+ u16 offset = le16_to_cpu(entry->e_value_offs);
+ void *p = bh->b_data + offset;
+
if (size > buffer_size)
goto cleanup;
- memcpy(buffer, bh->b_data + le16_to_cpu(entry->e_value_offs),
- size);
+ if (unlikely(p + size > end))
+ goto cleanup;
+ memcpy(buffer, p, size);
}
error = size;

@@ -370,12 +376,18 @@ ext4_xattr_ibody_get(struct inode *inode
if (error)
goto cleanup;
size = le32_to_cpu(entry->e_value_size);
+ error = -ERANGE;
+ if (unlikely(size > EXT4_XATTR_SIZE_MAX))
+ goto cleanup;
if (buffer) {
- error = -ERANGE;
+ u16 offset = le16_to_cpu(entry->e_value_offs);
+ void *p = (void *)IFIRST(header) + offset;
+
if (size > buffer_size)
goto cleanup;
- memcpy(buffer, (void *)IFIRST(header) +
- le16_to_cpu(entry->e_value_offs), size);
+ if (unlikely(p + size > end))
+ goto cleanup;
+ memcpy(buffer, p, size);
}
error = size;

--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -67,6 +67,17 @@ struct ext4_xattr_entry {
EXT4_I(inode)->i_extra_isize))
#define IFIRST(hdr) ((struct ext4_xattr_entry *)((hdr)+1))

+/*
+ * XATTR_SIZE_MAX is currently 64k, but for the purposes of checking
+ * for file system consistency errors, we use a somewhat bigger value.
+ * This allows XATTR_SIZE_MAX to grow in the future, but by using this
+ * instead of INT_MAX for certain consistency checks, we don't need to
+ * worry about arithmetic overflows. (Actually XATTR_SIZE_MAX is
+ * defined in include/uapi/linux/limits.h, so changing it is going
+ * not going to be trivial....)
+ */
+#define EXT4_XATTR_SIZE_MAX (1 << 24)
+
#define BHDR(bh) ((struct ext4_xattr_header *)((bh)->b_data))
#define ENTRY(ptr) ((struct ext4_xattr_entry *)(ptr))
#define BFIRST(bh) ENTRY(BHDR(bh)+1)