[RFC v2 2/5] blktrace: fix debugfs use after free
From: Luis Chamberlain
Date: Thu Apr 09 2020 - 17:45:46 EST
On commit 6ac93117ab00 ("blktrace: use existing disk debugfs directory")
merged on v4.12 Omar fixed the original blktrace code for multiqueue use.
This however left in place a possible crash, if you happen to abuse blktrace
in a way it was not intended.
Namely, if you loop adding a device, setup the blktrace with BLKTRACESETUP,
forget to BLKTRACETEARDOWN, and then just remove the device you end up
with a panic:
[ 107.193134] debugfs: Directory 'loop0' with parent 'block' already present!
[ 107.254615] BUG: kernel NULL pointer dereference, address: 00000000000000a0
[ 107.258785] #PF: supervisor write access in kernel mode
[ 107.262035] #PF: error_code(0x0002) - not-present page
[ 107.264106] PGD 0 P4D 0
[ 107.264404] Oops: 0002 [#1] SMP NOPTI
[ 107.264803] CPU: 8 PID: 674 Comm: kworker/8:2 Tainted: G E 5.6.0-rc7-next-20200327 #1
[ 107.265712] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
[ 107.266553] Workqueue: events __blk_release_queue
[ 107.267051] RIP: 0010:down_write+0x15/0x40
[ 107.267488] Code: eb ca e8 ee a5 8d ff cc cc cc cc cc cc cc cc cc cc cc cc cc cc 0f 1f 44 00 00 55 48 89 fd e8 52 db ff ff 31 c0 ba 01 00 00 00 <f0> 48 0f b1 55 00 75 0f 65 48 8b 04 25 c0 8b 01 00 48 89 45 08 5d
[ 107.269300] RSP: 0018:ffff9927c06efda8 EFLAGS: 00010246
[ 107.269841] RAX: 0000000000000000 RBX: ffff8be7e73b0600 RCX: ffffff8100000000
[ 107.270559] RDX: 0000000000000001 RSI: ffffff8100000000 RDI: 00000000000000a0
[ 107.271281] RBP: 00000000000000a0 R08: ffff8be7ebc80fa8 R09: ffff8be7ebc80fa8
[ 107.272001] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[ 107.272722] R13: ffff8be7efc30400 R14: ffff8be7e0571200 R15: 00000000000000a0
[ 107.273475] FS: 0000000000000000(0000) GS:ffff8be7efc00000(0000) knlGS:0000000000000000
[ 107.274346] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 107.274968] CR2: 00000000000000a0 CR3: 000000042abee003 CR4: 0000000000360ee0
[ 107.275710] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 107.276465] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 107.277214] Call Trace:
[ 107.277532] simple_recursive_removal+0x4e/0x2e0
[ 107.278049] ? debugfs_remove+0x60/0x60
[ 107.278493] debugfs_remove+0x40/0x60
[ 107.278922] blk_trace_free+0xd/0x50
[ 107.279339] __blk_trace_remove+0x27/0x40
[ 107.279797] blk_trace_shutdown+0x30/0x40
[ 107.280256] __blk_release_queue+0xab/0x110
[ 107.280734] process_one_work+0x1b4/0x380
[ 107.281194] worker_thread+0x50/0x3c0
[ 107.281622] kthread+0xf9/0x130
[ 107.281994] ? process_one_work+0x380/0x380
[ 107.282467] ? kthread_park+0x90/0x90
[ 107.282895] ret_from_fork+0x1f/0x40
[ 107.283316] Modules linked in: loop(E) <etc>
[ 107.288562] CR2: 00000000000000a0
[ 107.288957] ---[ end trace b885d243d441bbce ]---
This splat happens to be very similar to the one reported via
kernel.org korg#205713, only that korg#205713 was for v4.19.83
and the above now includes the simple_recursive_removal() introduced
via commit a3d1e7eb5abe ("simple_recursive_removal(): kernel-side rm
-rf for ramfs-style filesystems") merged on v5.6.
korg#205713 then was used to create CVE-2019-19770 and claims that
the bug is in a use-after-free in the debugfs core code. The
implications of this being a generic UAF on debugfs would be
much more severe, as it would imply parent dentries can sometimes
not be positive, which we hold by design is just not possible.
Below is the splat explained with a bit more details, explaining
what is happening in userspace, kernel, and a print of the CPU on,
which the code runs on:
load loopback module
[ 13.603371] == blk_mq_debugfs_register(12) start
[ 13.604040] == blk_mq_debugfs_register(12) q->debugfs_dir created
[ 13.604934] == blk_mq_debugfs_register(12) end
[ 13.627382] == blk_mq_debugfs_register(12) start
[ 13.628041] == blk_mq_debugfs_register(12) q->debugfs_dir created
[ 13.629240] == blk_mq_debugfs_register(12) end
[ 13.651667] == blk_mq_debugfs_register(12) start
[ 13.652836] == blk_mq_debugfs_register(12) q->debugfs_dir created
[ 13.655107] == blk_mq_debugfs_register(12) end
[ 13.684917] == blk_mq_debugfs_register(12) start
[ 13.687876] == blk_mq_debugfs_register(12) q->debugfs_dir created
[ 13.691588] == blk_mq_debugfs_register(13) end
[ 13.707320] == blk_mq_debugfs_register(13) start
[ 13.707863] == blk_mq_debugfs_register(13) q->debugfs_dir created
[ 13.708856] == blk_mq_debugfs_register(13) end
[ 13.735623] == blk_mq_debugfs_register(13) start
[ 13.736656] == blk_mq_debugfs_register(13) q->debugfs_dir created
[ 13.738411] == blk_mq_debugfs_register(13) end
[ 13.763326] == blk_mq_debugfs_register(13) start
[ 13.763972] == blk_mq_debugfs_register(13) q->debugfs_dir created
[ 13.765167] == blk_mq_debugfs_register(13) end
[ 13.779510] == blk_mq_debugfs_register(13) start
[ 13.780522] == blk_mq_debugfs_register(13) q->debugfs_dir created
[ 13.782338] == blk_mq_debugfs_register(13) end
[ 13.783521] loop: module loaded
LOOP_CTL_DEL(loop0) #1
[ 13.803550] = __blk_release_queue(4) start
[ 13.807772] == blk_trace_shutdown(4) start
[ 13.810749] == blk_trace_shutdown(4) end
[ 13.813437] = __blk_release_queue(4) calling blk_mq_debugfs_unregister()
[ 13.817593] ==== blk_mq_debugfs_unregister(4) begin
[ 13.817621] ==== blk_mq_debugfs_unregister(4) debugfs_remove_recursive(q->debugfs_dir)
[ 13.821203] ==== blk_mq_debugfs_unregister(4) end q->debugfs_dir is NULL
[ 13.826166] = __blk_release_queue(4) blk_mq_debugfs_unregister() end
[ 13.832992] = __blk_release_queue(4) end
LOOP_CTL_ADD(loop0) #1
[ 13.843742] == blk_mq_debugfs_register(7) start
[ 13.845569] == blk_mq_debugfs_register(7) q->debugfs_dir created
[ 13.848628] == blk_mq_debugfs_register(7) end
BLKTRACE_SETUP(loop0) #1
[ 13.850924] == blk_trace_ioctl(7, BLKTRACESETUP) start
[ 13.852852] === do_blk_trace_setup(7) start
[ 13.854580] === do_blk_trace_setup(7) creating directory
[ 13.856620] === do_blk_trace_setup(7) using what debugfs_lookup() gave
[ 13.860635] === do_blk_trace_setup(7) end with ret: 0
[ 13.862615] == blk_trace_ioctl(7, BLKTRACESETUP) end
LOOP_CTL_DEL(loop0) #2
[ 13.883304] = __blk_release_queue(7) start
[ 13.885324] == blk_trace_shutdown(7) start
[ 13.887197] == blk_trace_shutdown(7) calling __blk_trace_remove()
[ 13.889807] == __blk_trace_remove(7) start
[ 13.891669] === blk_trace_cleanup(7) start
[ 13.911656] ====== blk_trace_free(7) start
LOOP_CTL_ADD(loop0) #2
[ 13.912709] == blk_mq_debugfs_register(2) start
---> From LOOP_CTL_DEL(loop0) #2
[ 13.915887] ====== blk_trace_free(7) end
---> From LOOP_CTL_ADD(loop0) #2
[ 13.918359] debugfs: Directory 'loop0' with parent 'block' already present!
[ 13.926433] == blk_mq_debugfs_register(2) q->debugfs_dir created
[ 13.930373] == blk_mq_debugfs_register(2) end
BLKTRACE_SETUP(loop0) #2
[ 13.933961] == blk_trace_ioctl(2, BLKTRACESETUP) start
[ 13.936758] === do_blk_trace_setup(2) start
[ 13.938944] === do_blk_trace_setup(2) creating directory
[ 13.941029] === do_blk_trace_setup(2) using what debugfs_lookup() gave
---> From LOOP_CTL_DEL(loop0) #2
[ 13.971046] === blk_trace_cleanup(7) end
[ 13.973175] == __blk_trace_remove(7) end
[ 13.975352] == blk_trace_shutdown(7) end
[ 13.977415] = __blk_release_queue(7) calling blk_mq_debugfs_unregister()
[ 13.980645] ==== blk_mq_debugfs_unregister(7) begin
[ 13.980696] ==== blk_mq_debugfs_unregister(7) debugfs_remove_recursive(q->debugfs_dir)
[ 13.983118] ==== blk_mq_debugfs_unregister(7) end q->debugfs_dir is NULL
[ 13.986945] = __blk_release_queue(7) blk_mq_debugfs_unregister() end
[ 13.993155] = __blk_release_queue(7) end
---> From BLKTRACE_SETUP(loop0) #2
[ 13.995928] === do_blk_trace_setup(2) end with ret: 0
[ 13.997623] == blk_trace_ioctl(2, BLKTRACESETUP) end
LOOP_CTL_DEL(loop0) #3
[ 14.035119] = __blk_release_queue(2) start
[ 14.036925] == blk_trace_shutdown(2) start
[ 14.038518] == blk_trace_shutdown(2) calling __blk_trace_remove()
[ 14.040829] == __blk_trace_remove(2) start
[ 14.042413] === blk_trace_cleanup(2) start
LOOP_CTL_ADD(loop0) #3
[ 14.072522] == blk_mq_debugfs_register(6) start
---> From LOOP_CTL_DEL(loop0) #3
[ 14.075151] ====== blk_trace_free(2) start
---> From LOOP_CTL_ADD(loop0) #3
[ 14.075882] == blk_mq_debugfs_register(6) q->debugfs_dir created
---> From LOOP_CTL_DEL(loop0) #3
[ 14.078624] BUG: kernel NULL pointer dereference, address: 00000000000000a0
[ 14.084332] == blk_mq_debugfs_register(6) end
[ 14.086971] #PF: supervisor write access in kernel mode
[ 14.086974] #PF: error_code(0x0002) - not-present page
[ 14.086977] PGD 0 P4D 0
[ 14.086984] Oops: 0002 [#1] SMP NOPTI
[ 14.086990] CPU: 2 PID: 287 Comm: kworker/2:2 Tainted: G E 5.6.0-next-20200403+ #54
[ 14.086991] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
[ 14.087002] Workqueue: events __blk_release_queue
[ 14.087011] RIP: 0010:down_write+0x15/0x40
[ 14.090300] == blk_trace_ioctl(6, BLKTRACESETUP) start
[ 14.093277] Code: eb ca e8 3e 34 8d ff cc cc cc cc cc cc cc cc cc cc
cc cc cc cc 0f 1f 44 00 00 55 48 89 fd e8 52 db ff ff 31 c0 ba 01 00 00
00 <f0> 48 0f b1 55 00 75 0f 65 48 8b 04 25 c0 8b 01 00 48 89 45 08 5d
[ 14.093280] RSP: 0018:ffffc28a00533da8 EFLAGS: 00010246
[ 14.093284] RAX: 0000000000000000 RBX: ffff9f7a24d07980 RCX: ffffff8100000000
[ 14.093286] RDX: 0000000000000001 RSI: ffffff8100000000 RDI: 00000000000000a0
[ 14.093287] RBP: 00000000000000a0 R08: 0000000000000000 R09: 0000000000000019
[ 14.093289] R10: 0000000000000774 R11: 0000000000000000 R12: 0000000000000000
[ 14.093291] R13: ffff9f7a2fab0400 R14: ffff9f7a21dd1140 R15: 00000000000000a0
[ 14.093294] FS: 0000000000000000(0000) GS:ffff9f7a2fa80000(0000) knlGS:0000000000000000
[ 14.093296] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 14.093298] CR2: 00000000000000a0 CR3: 00000004293d2003 CR4: 0000000000360ee0
[ 14.093307] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 14.093308] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 14.093310] Call Trace:
[ 14.093324] simple_recursive_removal+0x4e/0x2e0
[ 14.093330] ? debugfs_remove+0x60/0x60
[ 14.093334] debugfs_remove+0x40/0x60
[ 14.093339] blk_trace_free+0x20/0x70
[ 14.093346] __blk_trace_remove+0x54/0x90
[ 14.096704] === do_blk_trace_setup(6) start
[ 14.098534] blk_trace_shutdown+0x74/0x80
[ 14.100958] === do_blk_trace_setup(6) creating directory
[ 14.104575] __blk_release_queue+0xbe/0x160
[ 14.104580] process_one_work+0x1b4/0x380
[ 14.104585] worker_thread+0x50/0x3c0
[ 14.104589] kthread+0xf9/0x130
[ 14.104593] ? process_one_work+0x380/0x380
[ 14.104596] ? kthread_park+0x90/0x90
[ 14.104599] ret_from_fork+0x1f/0x40
[ 14.104603] Modules linked in: loop(E) xfs(E) libcrc32c(E)
crct10dif_pclmul(E) crc32_pclmul(E) ghash_clmulni_intel(E) joydev(E)
serio_raw(E) aesni_intel(E) glue_helper(E) virtio_balloon(E) evdev(E)
crypto_simd(E) pcspkr(E) cryptd(E) i6300esb(E) button(E) ip_tables(E)
x_tables(E) autofs4(E) ext4(E) crc32c_generic(E) crc16(E) mbcache(E)
jbd2(E) virtio_net(E) net_failover(E) failover(E) virtio_blk(E)
ata_generic(E) uhci_hcd(E) ata_piix(E) ehci_hcd(E) nvme(E) libata(E)
crc32c_intel(E) usbcore(E) psmouse(E) nvme_core(E) virtio_pci(E)
scsi_mod(E) virtio_ring(E) t10_pi(E) virtio(E) i2c_piix4(E) floppy(E)
[ 14.107400] === do_blk_trace_setup(6) using what debugfs_lookup() gave
[ 14.108939] CR2: 00000000000000a0
[ 14.110589] === do_blk_trace_setup(6) end with ret: 0
[ 14.111592] ---[ end trace 7a783b33b9614db9 ]---
The root cause to this issue is that debugfs_lookup() can find a
previous incarnation's dir of the same name which is about to get
removed from a not yet schedule work.
We can fix the UAF by simply using a debugfs directory which moving
forward will always be accessible if debugfs is enabled, this way,
its allocated and avaialble always for both request-based block
drivers or make_request drivers (multiqueue) block drivers.
This simplifies the code considerably, with the only penalty now being
that we're always creating the request queue debugfs directory for the
request-based block device drivers.
The UAF then is not a core debugfs issue, but instead a misuse of
debugfs, and this issue can only be triggered if you are root, and
misuse blktrace.
This issue can be reproduced with break-blktrace [2] using:
break-blktrace -c 10 -d -s
This patch fixes this issue. Note that there is also another
respective UAF but from the ioctl path [3], this should also fix
that issue.
This patch then also disputes the severity of CVE-2019-19770 as
this issue is only possible by being root and using blktrace.
It is not a core debugfs issue.
[0] https://bugzilla.kernel.org/show_bug.cgi?id=205713
[1] https://nvd.nist.gov/vuln/detail/CVE-2019-19770
[2] https://github.com/mcgrof/break-blktrace
[3] https://lore.kernel.org/lkml/000000000000ec635b059f752700@xxxxxxxxxx/
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Omar Sandoval <osandov@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Nicolai Stange <nstange@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: yu kuai <yukuai3@xxxxxxxxxx>
Reported-by: syzbot+603294af2d01acfdd6da@xxxxxxxxxxxxxxxxxxxxxxxxx
Fiexes: 6ac93117ab00 ("blktrace: use existing disk debugfs directory")
Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
---
block/blk-debugfs.c | 12 ++++++++++++
block/blk-mq-debugfs.c | 5 -----
block/blk-sysfs.c | 3 +++
block/blk.h | 10 ++++++++++
include/linux/blkdev.h | 4 +++-
include/linux/blktrace_api.h | 1 -
kernel/trace/blktrace.c | 19 ++++++++-----------
7 files changed, 36 insertions(+), 18 deletions(-)
diff --git a/block/blk-debugfs.c b/block/blk-debugfs.c
index 634dea4b1507..a8b343e758e4 100644
--- a/block/blk-debugfs.c
+++ b/block/blk-debugfs.c
@@ -13,3 +13,15 @@ void blk_debugfs_register(void)
{
blk_debugfs_root = debugfs_create_dir("block", NULL);
}
+
+void blk_q_debugfs_register(struct request_queue *q)
+{
+ q->debugfs_dir = debugfs_create_dir(kobject_name(q->kobj.parent),
+ blk_debugfs_root);
+}
+
+void blk_q_debugfs_unregister(struct request_queue *q)
+{
+ debugfs_remove_recursive(q->debugfs_dir);
+ q->debugfs_dir = NULL;
+}
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index b3f2ba483992..bda9378eab90 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -823,9 +823,6 @@ void blk_mq_debugfs_register(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i;
- q->debugfs_dir = debugfs_create_dir(kobject_name(q->kobj.parent),
- blk_debugfs_root);
-
debugfs_create_files(q->debugfs_dir, q, blk_mq_debugfs_queue_attrs);
/*
@@ -856,9 +853,7 @@ void blk_mq_debugfs_register(struct request_queue *q)
void blk_mq_debugfs_unregister(struct request_queue *q)
{
- debugfs_remove_recursive(q->debugfs_dir);
q->sched_debugfs_dir = NULL;
- q->debugfs_dir = NULL;
}
static void blk_mq_debugfs_register_ctx(struct blk_mq_hw_ctx *hctx,
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index fca9b158f4a0..20f20b0fa0b9 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -895,6 +895,7 @@ static void __blk_release_queue(struct work_struct *work)
blk_trace_shutdown(q);
+ blk_q_debugfs_unregister(q);
if (queue_is_mq(q))
blk_mq_debugfs_unregister(q);
@@ -975,6 +976,8 @@ int blk_register_queue(struct gendisk *disk)
goto unlock;
}
+ blk_q_debugfs_register(q);
+
if (queue_is_mq(q)) {
__blk_mq_register_dev(dev, q);
blk_mq_debugfs_register(q);
diff --git a/block/blk.h b/block/blk.h
index 86a66b614f08..b86123a2d74f 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -489,10 +489,20 @@ int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
bool *same_page);
#ifdef CONFIG_DEBUG_FS
void blk_debugfs_register(void);
+void blk_q_debugfs_register(struct request_queue *q);
+void blk_q_debugfs_unregister(struct request_queue *q);
#else
static inline void blk_debugfs_register(void)
{
}
+
+static inline void blk_q_debugfs_register(struct request_queue *q)
+{
+}
+
+static inline void blk_q_debugfs_unregister(struct request_queue *q)
+{
+}
#endif /* CONFIG_DEBUG_FS */
#endif /* BLK_INTERNAL_H */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 32868fbedc9e..8b1cab52cef9 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -569,8 +569,10 @@ struct request_queue {
struct list_head tag_set_list;
struct bio_set bio_split;
-#ifdef CONFIG_BLK_DEBUG_FS
+#ifdef CONFIG_DEBUG_FS
struct dentry *debugfs_dir;
+#endif
+#ifdef CONFIG_BLK_DEBUG_FS
struct dentry *sched_debugfs_dir;
struct dentry *rqos_debugfs_dir;
#endif
diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h
index 3b6ff5902edc..eb6db276e293 100644
--- a/include/linux/blktrace_api.h
+++ b/include/linux/blktrace_api.h
@@ -22,7 +22,6 @@ struct blk_trace {
u64 end_lba;
u32 pid;
u32 dev;
- struct dentry *dir;
struct dentry *dropped_file;
struct dentry *msg_file;
struct list_head running_list;
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index ca39dc3230cb..15086227592f 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -311,7 +311,6 @@ static void blk_trace_free(struct blk_trace *bt)
debugfs_remove(bt->msg_file);
debugfs_remove(bt->dropped_file);
relay_close(bt->rchan);
- debugfs_remove(bt->dir);
free_percpu(bt->sequence);
free_percpu(bt->msg_data);
kfree(bt);
@@ -476,7 +475,6 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
struct blk_user_trace_setup *buts)
{
struct blk_trace *bt = NULL;
- struct dentry *dir = NULL;
int ret;
if (!buts->buf_size || !buts->buf_nr)
@@ -485,6 +483,9 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
if (!blk_debugfs_root)
return -ENOENT;
+ if (!q->debugfs_dir)
+ return -ENOENT;
+
strncpy(buts->name, name, BLKTRACE_BDEV_SIZE);
buts->name[BLKTRACE_BDEV_SIZE - 1] = '\0';
@@ -509,21 +510,19 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
ret = -ENOENT;
- dir = debugfs_lookup(buts->name, blk_debugfs_root);
- if (!dir)
- bt->dir = dir = debugfs_create_dir(buts->name, blk_debugfs_root);
-
bt->dev = dev;
atomic_set(&bt->dropped, 0);
INIT_LIST_HEAD(&bt->running_list);
ret = -EIO;
- bt->dropped_file = debugfs_create_file("dropped", 0444, dir, bt,
+ bt->dropped_file = debugfs_create_file("dropped", 0444,
+ q->debugfs_dir, bt,
&blk_dropped_fops);
- bt->msg_file = debugfs_create_file("msg", 0222, dir, bt, &blk_msg_fops);
+ bt->msg_file = debugfs_create_file("msg", 0222, q->debugfs_dir,
+ bt, &blk_msg_fops);
- bt->rchan = relay_open("trace", dir, buts->buf_size,
+ bt->rchan = relay_open("trace", q->debugfs_dir, buts->buf_size,
buts->buf_nr, &blk_relay_callbacks, bt);
if (!bt->rchan)
goto err;
@@ -551,8 +550,6 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
ret = 0;
err:
- if (dir && !bt->dir)
- dput(dir);
if (ret)
blk_trace_free(bt);
return ret;
--
2.25.1