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authorTakashi Iwai <tiwai@suse.de>2017-10-16 12:39:28 +0300
committerTakashi Iwai <tiwai@suse.de>2017-10-18 13:27:00 +0300
commita91d66129fb9bcead12af3ed2008d6ddbf179509 (patch)
treea11e4e5447a4fa58a1fac1e0a5e3f31128df52fd /sound/oss
parent6bf88a343db2b3c160edf9b82a74966b31cc80bd (diff)
downloadlinux-a91d66129fb9bcead12af3ed2008d6ddbf179509.tar.xz
ALSA: hda - Fix incorrect TLV callback check introduced during set_fs() removal
The commit 99b5c5bb9a54 ("ALSA: hda - Remove the use of set_fs()") converted the get_kctl_0dB_offset() call for killing set_fs() usage in HD-audio codec code. The conversion assumed that the TLV callback used in HD-audio code is only snd_hda_mixer_amp() and applies the TLV calculation locally. Although this assumption is correct, and all slave kctls are actually with that callback, the current code is still utterly buggy; it doesn't hit this condition and falls back to the next check. It's because the function gets called after adding slave kctls to vmaster. By assigning a slave kctl, the slave kctl object is faked inside vmaster code, and the whole kctl ops are overridden. Thus the callback op points to a different value from what we've assumed. More badly, as reported by the KERNEXEC and UDEREF features of PaX, the code flow turns into the unexpected pitfall. The next fallback check is SNDRV_CTL_ELEM_ACCESS_TLV_READ access bit, and this always hits for each kctl with TLV. Then it evaluates the callback function pointer wrongly as if it were a TLV array. Although currently its side-effect is fairly limited, this incorrect reference may lead to an unpleasant result. For addressing the regression, this patch introduces a new helper to vmaster code, snd_ctl_apply_vmaster_slaves(). This works similarly like the existing map_slaves() in hda_codec.c: it loops over the slave list of the given master, and applies the given function to each slave. Then the initializer function receives the right kctl object and we can compare the correct pointer instead of the faked one. Also, for catching the similar breakage in future, give an error message when the unexpected TLV callback is found and bail out immediately. Fixes: 99b5c5bb9a54 ("ALSA: hda - Remove the use of set_fs()") Reported-by: PaX Team <pageexec@freemail.hu> Cc: <stable@vger.kernel.org> # v4.13 Signed-off-by: Takashi Iwai <tiwai@suse.de>
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