mmc: vub300: fix use-after-free on probe failure

Overview

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

mmc: vub300: fix use-after-free on probe failure

The vub300 driver lifetime-manages its controller state using vub300->kref, with vub300_delete() freeing the mmc host when the last reference is dropped. The probe error path after the inactivity timer has been armed still bypasses that lifetime rule, however, and falls through to mmc_free_host() directly if mmc_add_host() fails.

The race window is between arming the inactivity timer and reaching the probe error unwind after mmc_add_host() fails:

    probe thread                     timer/workqueue
    ------------                     ---------------
    kref_init(&vub300->kref)         ref = 1
    kref_get(&vub300->kref)          ref = 2, timer ref
    add_timer(inactivity_timer)      fires after one second
    |
    |   race window
    |<---------------------------------------------------->
    |
    mmc_add_host(mmc)
                                     inactivity timer fires
                                     vub300_queue_dead_work()
                                       kref_get()          ref = 3
                                       queue_work(deadwork)
    mmc_add_host() fails
    timer_delete_sync()
    mmc_free_host(mmc)
      frees vub300
                                     deadwork runs
                                       use-after-free

The inactivity timeout is one second, so this would require mmc_add_host() to both fail and take more than one second to do so. This is unlikely to happen in practice, but the error path is still wrong.

timer_delete_sync() only waits for the timer callback itself. It does not flush deadwork that the callback may already have queued. As a result, queued deadwork can still hold a kref while the probe error path directly frees the backing mmc host, including the vub300 storage.

Fix this by using the same lifetime mechanism as disconnect. Clear vub300->interface so that the timer callback and any queued deadwork return early and drop their references, then drop the initial probe reference and return without falling through to err_free_host.

Affected

• Linux >= 0613ad2401f88bdeae5594c30afe318e93b14676 < face65f80c6946c631ca3490b4ebd2c016a4fd2c
• Linux >= 0613ad2401f88bdeae5594c30afe318e93b14676 < 6c66653dac9b25272d5fd4ed42a34aa5249e16df
• Linux >= 0613ad2401f88bdeae5594c30afe318e93b14676 < 5b82af744e06cd741938c3da54fdbe564a7e52d9
• Linux >= 0613ad2401f88bdeae5594c30afe318e93b14676 < 618cf6b139503ec18ef93ffd663396aaf99b763a
• Linux >= 0613ad2401f88bdeae5594c30afe318e93b14676 < a3b5f242997a3be7404112fd48784881560aea57
• Linux 41ed46bdbd2878cd6567abe0974a445f8b1b8ec8
• Linux 25f05d762ca5e1c685002a53dd44f68e78ca3feb
• Linux a46e681151bbdacdf6b89ee8c4e5bad0555142bb
• Linux 3b29f8769d32016b2d89183db4d80c7a71b7e35e
• Linux 3049a3b927a40d89d4582ff1033cd7953be773c7
• Linux afc898019e7bf18c5eb7a0ac19852fcb1b341b3c
• Linux c9e85979b59cb86f0a15defa8199d740e2b36b90
• Linux 2044b2ea77945f372ef161d1bbf814e471767ff2
• Linux >= 4.9.337 < 4.10
• Linux >= 4.14.303 < 4.15
• Linux >= 4.19.270 < 4.20
• Linux >= 5.4.229 < 5.5
• Linux >= 5.10.163 < 5.11
• Linux >= 5.15.86 < 5.16
• Linux >= 6.0.16 < 6.1
• Linux >= 6.1.2 < 6.2
• Linux 6.2

Remediation

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