Description of problem:
Ramon de Carvalho Valle was testing eCryptfs with fsfuzzer and ran across a stack overflow bug. At the beginning of each eCryptfs file, metadata is stored containing things like encrypted file encryption key (EFEK), key signature of key used to decrypt the EFEK, etc. This metadata is stored in "packets", as per RFC 2440 - OpenPGP Message Format.
The header of each packet contains a packet length field. As the eCryptfs kernel module reads the packet contents, it uses that packet length field in a memcpy() to the destination buffer. However, no checks existed to make sure the buffer was big enough to hold the entire packet contents.
A malicious user on the system that has permissions to perform an eCryptfs mount (root or setuid mount helper needed) can modify the metadata using hexedit and specify a bigger packet size than what the destination buffer can hold and also modify the packet contents, which would probably allow them to handcraft the data used to overwrite the stack.
Created attachment 354415 [details]
[PATCH 1/2] eCryptfs: Check Tag 11 literal data buffer size
kernel-18.104.22.168-217.2.3.fc11 has been submitted as an update for Fedora 11.
Common Vulnerabilities and Exposures assigned an identifier CVE-2009-2406 to
the following vulnerability:
Reference: BUGTRAQ:20090728 [RISE-2009002] Linux eCryptfs parse_tag_11_packet Literal Data Buffer Overflow Vulnerability
Reference: URL: http://www.securityfocus.com/archive/1/archive/1/505334/100/0/threaded
Reference: MISC: http://risesecurity.org/advisories/RISE-2009002.txt
Reference: CONFIRM: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6352a29305373ae6196491e6d4669f301e26492e
Reference: CONFIRM: http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-22.214.171.124
Reference: URL: http://www.debian.org/security/2009/dsa-1844
Reference: URL: http://www.debian.org/security/2009/dsa-1845
Reference: URL: http://www.ubuntu.com/usn/usn-807-1
Reference: URL: http://www.securityfocus.com/bid/35851
Reference: URL: http://secunia.com/advisories/35985
Reference: URL: http://secunia.com/advisories/36045
Reference: URL: http://secunia.com/advisories/36051
Reference: URL: http://secunia.com/advisories/36054
Reference: URL: http://www.vupen.com/english/advisories/2009/2041
Stack-based buffer overflow in the parse_tag_11_packet function in
fs/ecryptfs/keystore.c in the eCryptfs subsystem in the Linux kernel
before 126.96.36.199 allows local users to cause a denial of service
(system crash) or possibly gain privileges via vectors involving a
crafted eCryptfs file, related to not ensuring that the key signature
length in a Tag 11 packet is compatible with the key signature buffer
kernel-188.8.131.52-170.2.78.fc10 has been submitted as an update for Fedora 10.
This issue has been addressed in following products:
Red Hat Enterprise Linux 5
Via RHSA-2009:1193 https://rhn.redhat.com/errata/RHSA-2009-1193.html
kernel-184.108.40.206-170.2.78.fc10 has been pushed to the Fedora 10 stable repository. If problems still persist, please make note of it in this bug report.
kernel-220.127.116.11-217.2.3.fc11 has been pushed to the Fedora 11 stable repository. If problems still persist, please make note of it in this bug report.
Red Hat would like to thank Ramon de C. Valle for reporting this issue.