• Kees Cook's avatar
    ipc/mqueue.c: only perform resource calculation if user valid · 48c5c4f0
    Kees Cook authored
    [ Upstream commit a318f12ed8843cfac53198390c74a565c632f417 ]
    Andreas Christoforou reported:
      UBSAN: Undefined behaviour in ipc/mqueue.c:414:49 signed integer overflow:
      9 * 2305843009213693951 cannot be represented in type 'long int'
      Call Trace:
        mqueue_evict_inode+0x8e7/0xa10 ipc/mqueue.c:414
        evict+0x472/0x8c0 fs/inode.c:558
        iput_final fs/inode.c:1547 [inline]
        iput+0x51d/0x8c0 fs/inode.c:1573
        mqueue_get_inode+0x8eb/0x1070 ipc/mqueue.c:320
        mqueue_create_attr+0x198/0x440 ipc/mqueue.c:459
        vfs_mkobj+0x39e/0x580 fs/namei.c:2892
        prepare_open ipc/mqueue.c:731 [inline]
        do_mq_open+0x6da/0x8e0 ipc/mqueue.c:771
    Which could be triggered by:
            struct mq_attr attr = {
                    .mq_flags = 0,
                    .mq_maxmsg = 9,
                    .mq_msgsize = 0x1fffffffffffffff,
                    .mq_curmsgs = 0,
            if (mq_open("/testing", 0x40, 3, &attr) == (mqd_t) -1)
    mqueue_get_inode() was correctly rejecting the giant mq_msgsize, and
    preparing to return -EINVAL.  During the cleanup, it calls
    mqueue_evict_inode() which performed resource usage tracking math for
    updating "user", before checking if there was a valid "user" at all
    (which would indicate that the calculations would be sane).  Instead,
    delay this check to after seeing a valid "user".
    The overflow was real, but the results went unused, so while the flaw is
    harmless, it's noisy for kernel fuzzers, so just fix it by moving the
    calculation under the non-NULL "user" where it actually gets used.
    Link: http://lkml.kernel.org/r/201906072207.ECB65450@keescookSigned-off-by: default avatarKees Cook <keescook@chromium.org>
    Reported-by: default avatarAndreas Christoforou <andreaschristofo@gmail.com>
    Acked-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Cc: Manfred Spraul <manfred@colorfullife.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
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