ext4: add bounds checking to ext4_xattr_find_entry()

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>
Cc: stable@kernel.org

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index c030e41818abb3b6250c6fb4497f8fac45786c44..6304e81bfe6a800c93ba053ce939fcd84a672a77 100644 (file)
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -276,18 +276,22 @@ errout:
        __xattr_check_inode((inode), (header), (end), __func__, __LINE__)
 
 static int
-ext4_xattr_find_entry(struct ext4_xattr_entry **pentry, int name_index,
-                     const char *name, int sorted)
+xattr_find_entry(struct inode *inode, struct ext4_xattr_entry **pentry,
+                void *end, int name_index, const char *name, 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 -EFSCORRUPTED;
+               }
                cmp = name_index - entry->e_name_index;
                if (!cmp)
                        cmp = name_len - entry->e_name_len;
@@ -509,6 +513,7 @@ ext4_xattr_block_get(struct inode *inode, int name_index, const char *name,
        struct buffer_head *bh = NULL;
        struct ext4_xattr_entry *entry;
        size_t size;
+       void *end;
        int error;
        struct mb_cache *ea_block_cache = EA_BLOCK_CACHE(inode);
 
@@ -530,7 +535,8 @@ ext4_xattr_block_get(struct inode *inode, int name_index, const char *name,
                goto cleanup;
        ext4_xattr_block_cache_insert(ea_block_cache, bh);
        entry = BFIRST(bh);
-       error = ext4_xattr_find_entry(&entry, name_index, name, 1);
+       end = bh->b_data + bh->b_size;
+       error = xattr_find_entry(inode, &entry, end, name_index, name, 1);
        if (error)
                goto cleanup;
        size = le32_to_cpu(entry->e_value_size);
@@ -579,7 +585,7 @@ ext4_xattr_ibody_get(struct inode *inode, int name_index, const char *name,
        if (error)
                goto cleanup;
        entry = IFIRST(header);
-       error = ext4_xattr_find_entry(&entry, name_index, name, 0);
+       error = xattr_find_entry(inode, &entry, end, name_index, name, 0);
        if (error)
                goto cleanup;
        size = le32_to_cpu(entry->e_value_size);
@@ -1808,8 +1814,8 @@ ext4_xattr_block_find(struct inode *inode, struct ext4_xattr_info *i,
                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, 1);
+               error = xattr_find_entry(inode, &bs->s.here, bs->s.end,
+                                        i->name_index, i->name, 1);
                if (error && error != -ENODATA)
                        goto cleanup;
                bs->s.not_found = error;
@@ -2168,8 +2174,8 @@ int ext4_xattr_ibody_find(struct inode *inode, struct ext4_xattr_info *i,
                if (error)
                        return error;
                /* Find the named attribute. */
-               error = ext4_xattr_find_entry(&is->s.here, i->name_index,
-                                             i->name, 0);
+               error = xattr_find_entry(inode, &is->s.here, is->s.end,
+                                        i->name_index, i->name, 0);
                if (error && error != -ENODATA)
                        return error;
                is->s.not_found = error;