| Message ID | 20200608020557.31668-1-yanaijie@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4] block: Fix use-after-free in blkdev_get() | expand |
Looks good,
Reviewed-by: Christoph Hellwig <hch@lst.de>
Can you dig into the history for a proper fixes tag?
Hi Christoph, 在 2020/6/8 14:15, Christoph Hellwig 写道: > Looks good, > > Reviewed-by: Christoph Hellwig <hch@lst.de> > > Can you dig into the history for a proper fixes tag? > This one started to accessing bdev after __blkdev_get(). So I think it may be a proper fixes tag: Fixes: e525fd89d380 ("block: make blkdev_get/put() handle exclusive access") Thanks, Jason > . >
On Mon, Jun 8, 2020 at 8:18 AM Christoph Hellwig <hch@lst.de> wrote: > > Looks good, > > Reviewed-by: Christoph Hellwig <hch@lst.de> > > Can you dig into the history for a proper fixes tag? [ CC Dan ] Dan gave the hint for the Fixes: tag in reply to the first patch: > The Fixes tag is a good idea though: > > Fixes: 89e524c04fa9 ("loop: Fix mount(2) failure due to race with LOOP_SET_FD") > It broke last July. Before that, we used to check if __blkdev_get() > failed before dereferencing "bdev". - Sedat -
On Mon, Jun 8, 2020 at 8:47 AM Sedat Dilek <sedat.dilek@gmail.com> wrote: > > On Mon, Jun 8, 2020 at 8:18 AM Christoph Hellwig <hch@lst.de> wrote: > > > > Looks good, > > > > Reviewed-by: Christoph Hellwig <hch@lst.de> > > > > Can you dig into the history for a proper fixes tag? > > [ CC Dan ] > > Dan gave the hint for the Fixes: tag in reply to the first patch: > > > The Fixes tag is a good idea though: > > > > Fixes: 89e524c04fa9 ("loop: Fix mount(2) failure due to race with LOOP_SET_FD") > > > It broke last July. Before that, we used to check if __blkdev_get() > > failed before dereferencing "bdev". > Here is the Link. https://www.spinics.net/lists/linux-block/msg54825.html - Sedat -
On Mon, Jun 8, 2020 at 8:52 AM Sedat Dilek <sedat.dilek@gmail.com> wrote: > > On Mon, Jun 8, 2020 at 8:47 AM Sedat Dilek <sedat.dilek@gmail.com> wrote: > > > > On Mon, Jun 8, 2020 at 8:18 AM Christoph Hellwig <hch@lst.de> wrote: > > > > > > Looks good, > > > > > > Reviewed-by: Christoph Hellwig <hch@lst.de> > > > > > > Can you dig into the history for a proper fixes tag? > > > > [ CC Dan ] > > > > Dan gave the hint for the Fixes: tag in reply to the first patch: > > > > > The Fixes tag is a good idea though: > > > > > > Fixes: 89e524c04fa9 ("loop: Fix mount(2) failure due to race with LOOP_SET_FD") > > > > > It broke last July. Before that, we used to check if __blkdev_get() > > > failed before dereferencing "bdev". > > > > Here is the Link. > > https://www.spinics.net/lists/linux-block/msg54825.html > Really CC Dan in 3rd attempt. OMG, I need a coffee - urgently. - Sedat -
diff --git a/fs/block_dev.c b/fs/block_dev.c index 47860e589388..08c87db3a92b 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -1565,10 +1565,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) */ if (!for_part) { ret = devcgroup_inode_permission(bdev->bd_inode, perm); - if (ret != 0) { - bdput(bdev); + if (ret != 0) return ret; - } } restart: @@ -1637,8 +1635,10 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) goto out_clear; BUG_ON(for_part); ret = __blkdev_get(whole, mode, 1); - if (ret) + if (ret) { + bdput(whole); goto out_clear; + } bdev->bd_contains = whole; bdev->bd_part = disk_get_part(disk, partno); if (!(disk->flags & GENHD_FL_UP) || @@ -1688,7 +1688,6 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) disk_unblock_events(disk); put_disk_and_module(disk); out: - bdput(bdev); return ret; } @@ -1755,6 +1754,9 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder) bdput(whole); } + if (res) + bdput(bdev); + return res; } EXPORT_SYMBOL(blkdev_get);
In blkdev_get() we call __blkdev_get() to do some internal jobs and if there is some errors in __blkdev_get(), the bdput() is called which means we have released the refcount of the bdev (actually the refcount of the bdev inode). This means we cannot access bdev after that point. But acctually bdev is still accessed in blkdev_get() after calling __blkdev_get(). This results in use-after-free if the refcount is the last one we released in __blkdev_get(). Let's take a look at the following scenerio: CPU0 CPU1 CPU2 blkdev_open blkdev_open Remove disk bd_acquire blkdev_get __blkdev_get del_gendisk bdev_unhash_inode bd_acquire bdev_get_gendisk bd_forget failed because of unhashed bdput bdput (the last one) bdev_evict_inode access bdev => use after free [ 459.350216] BUG: KASAN: use-after-free in __lock_acquire+0x24c1/0x31b0 [ 459.351190] Read of size 8 at addr ffff88806c815a80 by task syz-executor.0/20132 [ 459.352347] [ 459.352594] CPU: 0 PID: 20132 Comm: syz-executor.0 Not tainted 4.19.90 #2 [ 459.353628] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 [ 459.354947] Call Trace: [ 459.355337] dump_stack+0x111/0x19e [ 459.355879] ? __lock_acquire+0x24c1/0x31b0 [ 459.356523] print_address_description+0x60/0x223 [ 459.357248] ? __lock_acquire+0x24c1/0x31b0 [ 459.357887] kasan_report.cold+0xae/0x2d8 [ 459.358503] __lock_acquire+0x24c1/0x31b0 [ 459.359120] ? _raw_spin_unlock_irq+0x24/0x40 [ 459.359784] ? lockdep_hardirqs_on+0x37b/0x580 [ 459.360465] ? _raw_spin_unlock_irq+0x24/0x40 [ 459.361123] ? finish_task_switch+0x125/0x600 [ 459.361812] ? finish_task_switch+0xee/0x600 [ 459.362471] ? mark_held_locks+0xf0/0xf0 [ 459.363108] ? __schedule+0x96f/0x21d0 [ 459.363716] lock_acquire+0x111/0x320 [ 459.364285] ? blkdev_get+0xce/0xbe0 [ 459.364846] ? blkdev_get+0xce/0xbe0 [ 459.365390] __mutex_lock+0xf9/0x12a0 [ 459.365948] ? blkdev_get+0xce/0xbe0 [ 459.366493] ? bdev_evict_inode+0x1f0/0x1f0 [ 459.367130] ? blkdev_get+0xce/0xbe0 [ 459.367678] ? destroy_inode+0xbc/0x110 [ 459.368261] ? mutex_trylock+0x1a0/0x1a0 [ 459.368867] ? __blkdev_get+0x3e6/0x1280 [ 459.369463] ? bdev_disk_changed+0x1d0/0x1d0 [ 459.370114] ? blkdev_get+0xce/0xbe0 [ 459.370656] blkdev_get+0xce/0xbe0 [ 459.371178] ? find_held_lock+0x2c/0x110 [ 459.371774] ? __blkdev_get+0x1280/0x1280 [ 459.372383] ? lock_downgrade+0x680/0x680 [ 459.373002] ? lock_acquire+0x111/0x320 [ 459.373587] ? bd_acquire+0x21/0x2c0 [ 459.374134] ? do_raw_spin_unlock+0x4f/0x250 [ 459.374780] blkdev_open+0x202/0x290 [ 459.375325] do_dentry_open+0x49e/0x1050 [ 459.375924] ? blkdev_get_by_dev+0x70/0x70 [ 459.376543] ? __x64_sys_fchdir+0x1f0/0x1f0 [ 459.377192] ? inode_permission+0xbe/0x3a0 [ 459.377818] path_openat+0x148c/0x3f50 [ 459.378392] ? kmem_cache_alloc+0xd5/0x280 [ 459.379016] ? entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 459.379802] ? path_lookupat.isra.0+0x900/0x900 [ 459.380489] ? __lock_is_held+0xad/0x140 [ 459.381093] do_filp_open+0x1a1/0x280 [ 459.381654] ? may_open_dev+0xf0/0xf0 [ 459.382214] ? find_held_lock+0x2c/0x110 [ 459.382816] ? lock_downgrade+0x680/0x680 [ 459.383425] ? __lock_is_held+0xad/0x140 [ 459.384024] ? do_raw_spin_unlock+0x4f/0x250 [ 459.384668] ? _raw_spin_unlock+0x1f/0x30 [ 459.385280] ? __alloc_fd+0x448/0x560 [ 459.385841] do_sys_open+0x3c3/0x500 [ 459.386386] ? filp_open+0x70/0x70 [ 459.386911] ? trace_hardirqs_on_thunk+0x1a/0x1c [ 459.387610] ? trace_hardirqs_off_caller+0x55/0x1c0 [ 459.388342] ? do_syscall_64+0x1a/0x520 [ 459.388930] do_syscall_64+0xc3/0x520 [ 459.389490] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 459.390248] RIP: 0033:0x416211 [ 459.390720] Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48 83 ec 08 e8 0a fa ff ff 48 89 04 24 b8 02 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fa ff ff 48 89 d0 48 83 c4 08 48 3d 01 [ 459.393483] RSP: 002b:00007fe45dfe9a60 EFLAGS: 00000293 ORIG_RAX: 0000000000000002 [ 459.394610] RAX: ffffffffffffffda RBX: 00007fe45dfea6d4 RCX: 0000000000416211 [ 459.395678] RDX: 00007fe45dfe9b0a RSI: 0000000000000002 RDI: 00007fe45dfe9b00 [ 459.396758] RBP: 000000000076bf20 R08: 0000000000000000 R09: 000000000000000a [ 459.397930] R10: 0000000000000075 R11: 0000000000000293 R12: 00000000ffffffff [ 459.399022] R13: 0000000000000bd9 R14: 00000000004cdb80 R15: 000000000076bf2c [ 459.400168] [ 459.400430] Allocated by task 20132: [ 459.401038] kasan_kmalloc+0xbf/0xe0 [ 459.401652] kmem_cache_alloc+0xd5/0x280 [ 459.402330] bdev_alloc_inode+0x18/0x40 [ 459.402970] alloc_inode+0x5f/0x180 [ 459.403510] iget5_locked+0x57/0xd0 [ 459.404095] bdget+0x94/0x4e0 [ 459.404607] bd_acquire+0xfa/0x2c0 [ 459.405113] blkdev_open+0x110/0x290 [ 459.405702] do_dentry_open+0x49e/0x1050 [ 459.406340] path_openat+0x148c/0x3f50 [ 459.406926] do_filp_open+0x1a1/0x280 [ 459.407471] do_sys_open+0x3c3/0x500 [ 459.408010] do_syscall_64+0xc3/0x520 [ 459.408572] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 459.409415] [ 459.409679] Freed by task 1262: [ 459.410212] __kasan_slab_free+0x129/0x170 [ 459.410919] kmem_cache_free+0xb2/0x2a0 [ 459.411564] rcu_process_callbacks+0xbb2/0x2320 [ 459.412318] __do_softirq+0x225/0x8ac Fix this by delaying bdput() to the end of blkdev_get() which means we have finished accessing bdev. Cc: Christoph Hellwig <hch@lst.de> Cc: Jens Axboe <axboe@kernel.dk> Cc: Ming Lei <ming.lei@redhat.com> Cc: Jan Kara <jack@suse.cz> Reported-by: Hulk Robot <hulkci@huawei.com> Signed-off-by: Jason Yan <yanaijie@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> --- v4: Remove uneeded braces and add Reviewed-by tag from Jan Kara. v3: Add bdput() when __blkdev_get() calling itself failed. v2: Add Reported-by tag and cc linux-block mailing list fs/block_dev.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)