dm ioctl: fix misbehavior if list_versions races with module loading

Overview

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

dm ioctl: fix misbehavior if list_versions races with module loading

__list_versions will first estimate the required space using the "dm_target_iterate(list_version_get_needed, &needed)" call and then will fill the space using the "dm_target_iterate(list_version_get_info, &iter_info)" call. Each of these calls locks the targets using the "down_read(&_lock)" and "up_read(&_lock)" calls, however between the first and second "dm_target_iterate" there is no lock held and the target modules can be loaded at this point, so the second "dm_target_iterate" call may need more space than what was the first "dm_target_iterate" returned.

The code tries to handle this overflow (see the beginning of list_version_get_info), however this handling is incorrect.

The code sets "param->data_size = param->data_start + needed" and "iter_info.end = (char *)vers+len" - "needed" is the size returned by the first dm_target_iterate call; "len" is the size of the buffer allocated by userspace.

"len" may be greater than "needed"; in this case, the code will write up to "len" bytes into the buffer, however param->data_size is set to "needed", so it may write data past the param->data_size value. The ioctl interface copies only up to param->data_size into userspace, thus part of the result will be truncated.

Fix this bug by setting "iter_info.end = (char *)vers + needed;" - this guarantees that the second "dm_target_iterate" call will write only up to the "needed" buffer and it will exit with "DM_BUFFER_FULL_FLAG" if it overflows the "needed" space - in this case, userspace will allocate a larger buffer and retry.

Note that there is also a bug in list_version_get_needed - we need to add "strlen(tt->name) + 1" to the needed size, not "strlen(tt->name)".

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 0c8d4112df329bf3dfbf27693f918c3b08676538
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6a818db0d5aecf80d4ba9e10ac153f60adc629ca
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 3a1c35d72dc0b34d1e746ed705790c0f630aa427
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < b545c0e1e4094d4de2bdfe9a3823f9154b0c0005
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < f59f5a269ca5e43c567aca7f1f52500a0186e9b7
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6ffce7a92ef5c68f7e5d6f4d722c2f96280c064b
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 5398b8e275bf81a2517b327d216c0f37ac9ac5ae
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 4fe1ec995483737f3d2a14c3fe1d8fe634972979
• Linux 2.6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.