[PATCH 3.16 082/366] ext4: add bounds checking to ext4_xattr_find_entry()

Ben Hutchings
2018-10-14T23:28:24Z

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

commit 9496005d6ca4cf8f5ee8f828165a8956872dc59d upstream.

Add some paranoia checks to make sure we don't stray beyond the end of
the valid memory region containing ext4 xattr entries while we are
scanning for a match.

Also rename the function to xattr_find_entry() since it is static and
thus only used in fs/ext4/xattr.c

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16:
- Keep passing an explicit size to xattr_find_entry()
- s/EFSCORRUPTED/EIO/]]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/xattr.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -240,18 +240,23 @@ ext4_xattr_check_entry(struct ext4_xattr
}

static int
-ext4_xattr_find_entry(struct ext4_xattr_entry **pentry, int name_index,
- const char *name, size_t size, int sorted)
+xattr_find_entry(struct inode *inode, struct ext4_xattr_entry **pentry,
+ void *end, int name_index, const char *name, size_t size,
+ int sorted)
{
- struct ext4_xattr_entry *entry;
+ struct ext4_xattr_entry *entry, *next;
size_t name_len;
int cmp = 1;

if (name == NULL)
return -EINVAL;
name_len = strlen(name);
- entry = *pentry;
- for (; !IS_LAST_ENTRY(entry); entry = EXT4_XATTR_NEXT(entry)) {
+ for (entry = *pentry; !IS_LAST_ENTRY(entry); entry = next) {
+ next = EXT4_XATTR_NEXT(entry);
+ if ((void *) next >= end) {
+ EXT4_ERROR_INODE(inode, "corrupted xattr entries");
+ return -EIO;
+ }
cmp = name_index - entry->e_name_index;
if (!cmp)
cmp = name_len - entry->e_name_len;
@@ -273,6 +278,7 @@ ext4_xattr_block_get(struct inode *inode
struct buffer_head *bh = NULL;
struct ext4_xattr_entry *entry;
size_t size;
+ void *end;
int error;
struct mb_cache *ext4_mb_cache = EXT4_GET_MB_CACHE(inode);

@@ -298,7 +304,9 @@ bad_block:
}
ext4_xattr_cache_insert(ext4_mb_cache, bh);
entry = BFIRST(bh);
- error = ext4_xattr_find_entry(&entry, name_index, name, bh->b_size, 1);
+ end = bh->b_data + bh->b_size;
+ error = xattr_find_entry(inode, &entry, end, name_index, name,
+ bh->b_size, 1);
if (error == -EIO)
goto bad_block;
if (error)
@@ -342,8 +350,8 @@ ext4_xattr_ibody_get(struct inode *inode
error = ext4_xattr_check_names(entry, end, entry);
if (error)
goto cleanup;
- error = ext4_xattr_find_entry(&entry, name_index, name,
- end - (void *)entry, 0);
+ error = xattr_find_entry(inode, &entry, end, name_index, name,
+ end - (void *)entry, 0);
if (error)
goto cleanup;
size = le32_to_cpu(entry->e_value_size);
@@ -761,8 +769,9 @@ ext4_xattr_block_find(struct inode *inod
bs->s.first = BFIRST(bs->bh);
bs->s.end = bs->bh->b_data + bs->bh->b_size;
bs->s.here = bs->s.first;
- error = ext4_xattr_find_entry(&bs->s.here, i->name_index,
- i->name, bs->bh->b_size, 1);
+ error = xattr_find_entry(inode, &bs->s.here, bs->s.end,
+ i->name_index, i->name,
+ bs->bh->b_size, 1);
if (error && error != -ENODATA)
goto cleanup;
bs->s.not_found = error;
@@ -1007,9 +1016,9 @@ int ext4_xattr_ibody_find(struct inode *
if (error)
return error;
/* Find the named attribute. */
- error = ext4_xattr_find_entry(&is->s.here, i->name_index,
- i->name, is->s.end -
- (void *)is->s.base, 0);
+ error = xattr_find_entry(inode, &is->s.here, is->s.end,
+ i->name_index, i->name,
+ is->s.end - (void *)is->s.base, 0);
if (error && error != -ENODATA)
return error;
is->s.not_found = error;