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authorVegard Nossum <vegard.nossum@oracle.com>2016-08-28 10:13:07 +0200
committerTakashi Iwai <tiwai@suse.de>2016-09-02 15:13:08 +0200
commit11749e086b2766cccf6217a527ef5c5604ba069c (patch)
tree6a503f6007a133eeb3a3918f910c0605d88e21e9 /sound
parent6b1ca4bcadf9ef077cc5f03c6822ba276ed14902 (diff)
downloadlinux-stericsson-11749e086b2766cccf6217a527ef5c5604ba069c.tar.gz
ALSA: timer: fix NULL pointer dereference in read()/ioctl() race
I got this with syzkaller: ================================================================== BUG: KASAN: null-ptr-deref on address 0000000000000020 Read of size 32 by task syz-executor/22519 CPU: 1 PID: 22519 Comm: syz-executor Not tainted 4.8.0-rc2+ #169 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2 014 0000000000000001 ffff880111a17a00 ffffffff81f9f141 ffff880111a17a90 ffff880111a17c50 ffff880114584a58 ffff880114584a10 ffff880111a17a80 ffffffff8161fe3f ffff880100000000 ffff880118d74a48 ffff880118d74a68 Call Trace: [<ffffffff81f9f141>] dump_stack+0x83/0xb2 [<ffffffff8161fe3f>] kasan_report_error+0x41f/0x4c0 [<ffffffff8161ff74>] kasan_report+0x34/0x40 [<ffffffff82c84b54>] ? snd_timer_user_read+0x554/0x790 [<ffffffff8161e79e>] check_memory_region+0x13e/0x1a0 [<ffffffff8161e9c1>] kasan_check_read+0x11/0x20 [<ffffffff82c84b54>] snd_timer_user_read+0x554/0x790 [<ffffffff82c84600>] ? snd_timer_user_info_compat.isra.5+0x2b0/0x2b0 [<ffffffff817d0831>] ? proc_fault_inject_write+0x1c1/0x250 [<ffffffff817d0670>] ? next_tgid+0x2a0/0x2a0 [<ffffffff8127c278>] ? do_group_exit+0x108/0x330 [<ffffffff8174653a>] ? fsnotify+0x72a/0xca0 [<ffffffff81674dfe>] __vfs_read+0x10e/0x550 [<ffffffff82c84600>] ? snd_timer_user_info_compat.isra.5+0x2b0/0x2b0 [<ffffffff81674cf0>] ? do_sendfile+0xc50/0xc50 [<ffffffff81745e10>] ? __fsnotify_update_child_dentry_flags+0x60/0x60 [<ffffffff8143fec6>] ? kcov_ioctl+0x56/0x190 [<ffffffff81e5ada2>] ? common_file_perm+0x2e2/0x380 [<ffffffff81746b0e>] ? __fsnotify_parent+0x5e/0x2b0 [<ffffffff81d93536>] ? security_file_permission+0x86/0x1e0 [<ffffffff816728f5>] ? rw_verify_area+0xe5/0x2b0 [<ffffffff81675355>] vfs_read+0x115/0x330 [<ffffffff81676371>] SyS_read+0xd1/0x1a0 [<ffffffff816762a0>] ? vfs_write+0x4b0/0x4b0 [<ffffffff82001c2c>] ? __this_cpu_preempt_check+0x1c/0x20 [<ffffffff8150455a>] ? __context_tracking_exit.part.4+0x3a/0x1e0 [<ffffffff816762a0>] ? vfs_write+0x4b0/0x4b0 [<ffffffff81005524>] do_syscall_64+0x1c4/0x4e0 [<ffffffff810052fc>] ? syscall_return_slowpath+0x16c/0x1d0 [<ffffffff83c3276a>] entry_SYSCALL64_slow_path+0x25/0x25 ================================================================== There are a couple of problems that I can see: - ioctl(SNDRV_TIMER_IOCTL_SELECT), which potentially sets tu->queue/tu->tqueue to NULL on memory allocation failure, so read() would get a NULL pointer dereference like the above splat - the same ioctl() can free tu->queue/to->tqueue which means read() could potentially see (and dereference) the freed pointer We can fix both by taking the ioctl_lock mutex when dereferencing ->queue/->tqueue, since that's always held over all the ioctl() code. Just looking at the code I find it likely that there are more problems here such as tu->qhead pointing outside the buffer if the size is changed concurrently using SNDRV_TIMER_IOCTL_PARAMS. Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/timer.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/sound/core/timer.c b/sound/core/timer.c
index 2d6e3e76ddf5..2706061fc1ea 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1972,6 +1972,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
tu->qused--;
spin_unlock_irq(&tu->qlock);
+ mutex_lock(&tu->ioctl_lock);
if (tu->tread) {
if (copy_to_user(buffer, &tu->tqueue[qhead],
sizeof(struct snd_timer_tread)))
@@ -1981,6 +1982,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
sizeof(struct snd_timer_read)))
err = -EFAULT;
}
+ mutex_unlock(&tu->ioctl_lock);
spin_lock_irq(&tu->qlock);
if (err < 0)