Description

In the Linux kernel, the following vulnerability has been resolved: virtio_net: Fix misalignment bug in struct virtnet_info Use the new TRAILING_OVERLAP() helper to fix a misalignment bug along with the following warning: drivers/net/virtio_net.c:429:46: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] This helper creates a union between a flexible-array member (FAM) and a set of members that would otherwise follow it (in this case `u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];`). This overlays the trailing members (rss_hash_key_data) onto the FAM (hash_key_data) while keeping the FAM and the start of MEMBERS aligned. The static_assert() ensures this alignment remains. Notice that due to tail padding in flexible `struct virtio_net_rss_config_trailer`, `rss_trailer.hash_key_data` (at offset 83 in struct virtnet_info) and `rss_hash_key_data` (at offset 84 in struct virtnet_info) are misaligned by one byte. See below: struct virtio_net_rss_config_trailer { __le16 max_tx_vq; /* 0 2 */ __u8 hash_key_length; /* 2 1 */ __u8 hash_key_data[]; /* 3 0 */ /* size: 4, cachelines: 1, members: 3 */ /* padding: 1 */ /* last cacheline: 4 bytes */ }; struct virtnet_info { ... struct virtio_net_rss_config_trailer rss_trailer; /* 80 4 */ /* XXX last struct has 1 byte of padding */ u8 rss_hash_key_data[40]; /* 84 40 */ ... /* size: 832, cachelines: 13, members: 48 */ /* sum members: 801, holes: 8, sum holes: 31 */ /* paddings: 2, sum paddings: 5 */ }; After changes, those members are correctly aligned at offset 795: struct virtnet_info { ... union { struct virtio_net_rss_config_trailer rss_trailer; /* 792 4 */ struct { unsigned char __offset_to_hash_key_data[3]; /* 792 3 */ u8 rss_hash_key_data[40]; /* 795 40 */ }; /* 792 43 */ }; /* 792 44 */ ... /* size: 840, cachelines: 14, members: 47 */ /* sum members: 801, holes: 8, sum holes: 35 */ /* padding: 4 */ /* paddings: 1, sum paddings: 4 */ /* last cacheline: 8 bytes */ }; As a result, the RSS key passed to the device is shifted by 1 byte: the last byte is cut off, and instead a (possibly uninitialized) byte is added at the beginning. As a last note `struct virtio_net_rss_config_hdr *rss_hdr;` is also moved to the end, since it seems those three members should stick around together. :)

Metrics

 

CVSS Version 4.0 CVSS Version 3.x CVSS Version 2.0

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CVSS 4.0 Severity and Vector Strings:

NIST: NVD

N/A

NVD assessment not yet provided.

CVSS 3.x Severity and Vector Strings:

NIST: NVD

Base Score:  N/A

NVD assessment not yet provided.

CVSS 2.0 Severity and Vector Strings:

NIST: NVD

Base Score: N/A

NVD assessment not yet provided.

In the Linux kernel, the following vulnerability has been resolved:

virtio_net: Fix misalignment bug in struct virtnet_info

Use the new TRAILING_OVERLAP() helper to fix a misalignment bug
along with the following warning:

drivers/net/virtio_net.c:429:46: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM)
and a set of members that would otherwise follow it (in this case
`u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];`). This
overlays the trailing members (rss_hash_key_data) onto the FAM
(hash_key_data) while keeping the FAM and the start of MEMBERS aligned.
The static_assert() ensures this alignment remains.

Notice that due to tail padding in flexible `struct
virtio_net_rss_config_trailer`, `rss_trailer.hash_key_data`
(at offset 83 in struct virtnet_info) and `rss_hash_key_data` (at
offset 84 in struct virtnet_info) are misaligned by one byte. See
below:

struct virtio_net_rss_config_trailer {
        __le16                     max_tx_vq;            /*     0     2 */
        __u8                       hash_key_length;      /*     2     1 */
        __u8                       hash_key_data[];      /*     3     0 */

        /* size: 4, cachelines: 1, members: 3 */
        /* padding: 1 */
        /* last cacheline: 4 bytes */
};

struct virtnet_info {
...
        struct virtio_net_rss_config_trailer rss_trailer; /*    80     4 */

        /* XXX last struct has 1 byte of padding */

        u8                         rss_hash_key_data[40]; /*    84    40 */
...
        /* size: 832, cachelines: 13, members: 48 */
        /* sum members: 801, holes: 8, sum holes: 31 */
        /* paddings: 2, sum paddings: 5 */
};

After changes, those members are correctly aligned at offset 795:

struct virtnet_info {
...
        union {
                struct virtio_net_rss_config_trailer rss_trailer; /*   792     4 */
                struct {
                        unsigned char __

https://git.kernel.org/stable/c/4156c3745f06bc197094b9ee97a9584e69ed00bf

https://git.kernel.org/stable/c/ae48108c2310f1dd700e0dbb655c2f1d92ed00fc