CVE-2011-2203: Null Pointer Dereference
First published: Mon Jun 13 2011(Updated: )
hfs_find_init() is wrongly assuming that sb->ext_tree has already been opened and is not NULL but this function can be called when sb->ext_tree is currently being opened (NULL deref). Indeed when we have the following call path, the NULL deref. occurs: In hfs_mdb_get() we have (at this stage ext_tree == NULL): HFS_SB(sb)->ext_tree = hfs_btree_open(sb, HFS_EXT_CNID, hfs_ext_keycmp); hfs_btree_open() is calling read_mapping_page() which is indirectly a call to hfs_readpage(). Then hfs_readpage() can make the following calls: hfs_readpage() -> hfs_get_block() -> alloc_buffer_head() -> hfs_ext_read_extent() Then hfs_ext_read_extent() calls hfs_find_init() with an ext_tree == NULL. Then we have a NULL dereference in hfs_find_init(). ptr = kmalloc(tree->max_key_len (...)); Due to the huge call stack from hfs_btree_open() to hfs_find_init() there are many ways to fix this dereference but I can't find the proper way to fix it. Moreover if we look at the code in hfs_find_init(). 20 ptr = kmalloc(tree->max_key_len * 2 + 4, GFP_KERNEL); 21 if (!ptr) 22 return -ENOMEM; 23 fd->search_key = ptr; 24 fd->key = ptr + tree->max_key_len + 2; We can make "max_key_len * 2 + 4" wrap and have an fd->key pointing outside of the kmalloc()'ed space. Moreover we can make space in fd->search_key lower than max_key_len and bad things can occur. Reference: <a href="https://lkml.org/lkml/2011/6/8/154">https://lkml.org/lkml/2011/6/8/154</a> Acknowledgements: Red Hat would like to thank Clement Lecigne for reporting this issue.
Credit: secalert@redhat.com secalert@redhat.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Linux kernel | =2.6 | |
| debian/linux-2.6 |
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Reference Links
- http://www.securityfocus.com/bid/48236
- https://lkml.org/lkml/2011/6/8/154
- https://bugzilla.redhat.com/show_bug.cgi?id=712774
- http://www.openwall.com/lists/oss-security/2011/06/13/16
- http://www.ubuntu.com/usn/USN-1328-1
- http://www.ubuntu.com/usn/USN-1324-1
- http://www.ubuntu.com/usn/USN-1344-1
- http://secunia.com/advisories/47754
- https://rhn.redhat.com/errata/RHSA-2011-1479.html
- https://access.redhat.com/support/policy/updates/errata/
- http://groups.google.com/group/linux.kernel/browse_thread/thread/031d20158467229f?pli=1
- http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commit;h=434a964daa14b9db083ce20404a4a2add54d037a
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=782695
- https://launchpad.net/bugs/cve/CVE-2011-2203
- https://security-tracker.debian.org/tracker/CVE-2011-2203
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-2203
- https://nvd.nist.gov/vuln/detail/CVE-2011-2203
- https://ubuntu.com/security/CVE-2011-2203
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